Yojamba Isle is a small island, home to the Zandalar Tribe. It is located in the northwestern corner of Stranglethorn Vale, near the border with Westfall and northwest of the Haunted Isle and The Vile Reef. This is the primary location for information, quests, and rewards related to Zul'Gurub.
From here, one may receive quests to go into Zul'Gurub and get certain items. When these items are in your possession and you have high enough reputation, you may turn in the quest for rewards. Also, at friendly reputation, you may receive, free of charge, a necklace from your class master on the island (the one who gives the class-specific quests). Return to the class master at each new reputation level for an upgrade to the necklace.
There is also a vendor that sells high-level crafting profession recipes, for which you must have the correct reputation. You can also turn in honor tokens to purchase Zanza potions at revered and shoulder enchants at exalted.
Hakkari Bijous and Zul'Gurub Coins can be turned in for bonus reputation instead of used in the quests. Take bijous to the altar on the island and right click them. They will be destroyed and you will gain a good amount of reputation. Turn in coins in groups of three outside the altar for extra reputation.