After collecting the debt from the troublesome business owners in "Taking Care of Business", Brynjolf asks you to follow him, which begins the next Thieves Guild quest, "Loud and Clear"

Loud and Clear
Brynjolf is taking me to meet the leader of the organization he represents. He says more and significantly more coin could be available if I join their ranks.

Follow Byrnjolf

Follow him, as he leads you into the Ragged Flagon Cistern. The quest log updates:

"Thanks to Brynjolf's support, I've been welcomed into the Thieves Guild by its Guild Master, Mercer Frey. I'm eager to receive my first task and prove that his recommendation wasn't in vain"

Brynjolf introduces you to Mercer as the New Recruit. Listen to Mercer Frey. Mercer will tell you that if you play by the rules, you will walk away rich. You break the rules, and you lose your share. You do what they say, and when they say, no debate or discussion. If you try arguing why you need rules if you are thieves, he becomes upset but will let the comment slide because you are new here. Tell him you understand. He now wants to put your expertise to the test.

He tells you about Goldenglow estate which is critically important to one of their larger clients. However, the owner has suddenly decided to take matters into his own hand and shut them out. He needs to be taught a lesson. Brynjolf will provide you with the details. Mercer then welcomes you to the Guild as a member!

Ask Byrnjolf how to get your cut of the spoils. He will tell you to do what you are told and keep your blade clean, and suggests you talk to Delvin Mallory and Vex for tips or to get more jobs, as well as to Tonilia who can set you up with equipment and supplies.

Ask Byrnjolf to tell you about the Goldenglow job. He will tell you its a bee farm owned by a wood elf named Aringolf. He wants you to teach him a lesson by burning down three of the estate's hives and clearing the safe in the house. The catch is that you cannot burn the whole place to the ground. Tell him it makes sense, and ask him what you should do about Aringoth. He will tell you that Maven prefers to keep him alive, but if he causes trouble then kill him.

Ask him how to destroy the beehives. He will tell you that their weakness is flames .But Maven Black-Briar doesn't want you  to level the whole estate. Ask him for more details on the estate. He will say they used to extort it, but Aringoth suddenly put a stop to it and hired mercenaries to guard the estate. Vex hardly made it out of there alive. You should talk to her before you go in.

Head back to the Ragged Flaggon and talk to Vex. Tell her you heard she ran into trouble at Goldenglow. She will tell you the wood elf had tripled the guard on the estate. Ask her for tips to get you in there. She will tell you  there is an old sewer tunnel that dumps into a lake on the northwest side of the island. That is how she slipped in there. And it should still be unguarded.

Vex can also train you in lockpicking and give you break in and burglary jobs.

Check yout quest log:
My first task as a member of the thieves guild involves a honey operation located just outside Riften called Goldenglow Estate. My actions there are in direct response to the Owner's sudden silence and lack of cooperation with the Thieves Guild and Maven Black-Briar, one of the Guild's most important clients.

(Optional) Enter Goldenglow using sewer
(Optional) Speak to Vex about Goldenglow Estate
Clear out Aringoth's safe
Burn three bee hives (0/3)

Talk to Tonilia. She is the fence of the thieves guild, she will buy from you whatever you whatever stolen goods you manage to steal. She will also set you up with a Thieves Guild armor set (Free). The Thieves Guild Armor increases carrying capacity by 20 points. The boots give you a 15% higher pickpocket success, and the gloves make lockpicking easier. Hood makes prices be 10% better.
Talk to Delvin to learn more about the thieves guild. He can also train you in sneaking and give you numbers jobs and fishing jobs.

Go back to the Cistern and exit to Riften through the ladder to the SW. Then pull the chain to open the plate above. You will now have discovered the Thieves Guild and can fast travel to it from now on. Head north and exit Riften to Skyrim

Bring up the map and look for the destination markers. Go around the town to the south, and take the road past Snow Shod Farm. In the map, you will see two small islands in the center of the lake.  The sewer entrance is on the NW side of the island to the NE. Use it to infiltrate the estate, as suggested by Vex

The sewers won't be guarded, but there will be rats and traps. Be careful when being beaten by a Skeever, as you could contract Ataxia and suffer from reduced lockpicking and pickpocketing. If that happens, go to a shrine or drink a cure disease potion as soon as you have the opportunity,

Work your way east through the sewers. In a chamber to the south, an adept lock will guard a treasure chest with some gold in it, so pick the lock if you can. Then go back to the corridor and keep heading east. Emerge at a ladder in the end of the tunnel.

Pick the lock on the door outside. It's an expert lock so could be tough - save your game before attempting so that you do not lose too many lockpicks. Or, you could kill the guards and find a key to the estate. As you enter, you get another objective - to obtain the key to Aringoth's safe, since that safe is hard to open. There is a storage room (behind an adept lock) with a potion of pickpocketing (making it 20% easier for 60 seconds) and a couple of chests. A room to the south has 3 mercenaries, so be careful not to be spotted or be prepared to take them down. Help yourself to valuable items around the house.

To the Southeast, behind a gate with a novice lock, stairs lead down to the basement where the Safe is. But first you could go up to the second floor instead, and retrieve the key from Aringoth. The stairs to the 2nd floor are just across the gate.

Climb to the 2nd floor, and locate  a novice door in a bedroom to the center. Open it, Aringoth is inside. You can try sneaking up on him and pickpocketing the goldenglow safe key as well as the goldenglow cellar key. You could try to PERSUADE him to give you the key. Or you can just fight and kill him, since in your briefing you were told that it is ok to kill him if he gets in the way.

After dealing with Aringof, head down to the cellar and locate the safe in the basement. If you have Aringof's key, you can immediately unlock the safe. Otherwise pick it (EXPERT LOCK).  You can then exit from the sewer grate below and head to the ladder to come out to Skyrim.

Now it's time to burn the beehives (you could have also burnt them before you dealt with the safe, if you wanted. If this is the case, just return to  Brynjolf to complete this quest). You need three of them burnt.

To burn the bee hives, you can either equip a torch from nearby, or use a flames spell (every race starts with it even if you are not a mage - so check your magic menu). This will probably attract the attention of additional mercenaries, so be prepared to either make a getaway or fight them.

Fast Travel to the Riften Thieves Guild. Press the button on the coffin to open the grate.  Report to Brynjolf at the Ragged Flagon. Give him the Goldenglow Bill of Sale you found in the safe. He is happy with your work. He tells you Maven Black Briar wants to see you.
"I've completed my task at Goldenglow Estate and discovered the owner's sudden lack of cooperation with the guild was leveraged by an anonymous buyer of that very same location. Why this buyer purchased Goldenglow and is showing animosity towards the guild is a mystery for the moment.

Brynjolf gives your reward. This completes the quest "Loud and Clear" and starts the next Thieves Guild Quest, "Dampened Spirits".