I am trying to create a mod, that adds a shopkeeper. On the shopkeeper gui, i just want a button to give the player an item like dirt, when the player clicks it gives them dirt. Ive set up everything but i dont know how to give the player an item, is there like entity.player.giveItem? or something like that

First of all, you should understand that GUIs and such are CLIENT side, and that you should never try to change something, such as a player's inventory, on the client side.

 

So you will need to send a packet when your button is clicked with information about which item the player was asking for, and when the server receives this packet, you can decide if the player is allowed to be given the item.

 

To add an item to a player's inventory, you can use player.inventory.addItemStackToInventory(ItemStack).

For information on packets, here is the best tutorial:

http://www.minecraftforge.net/forum/index.php/topic,20135.0.html

You sir, are very majestic thanks!

One more thing how would one go about rendering an icon on a GUI like when a dirt block is on the floor i want that same image and movement on the gui.

If I'm understanding what you want, itemRender.renderItemIntoGUI should do fine.