Besides apply, a HUD button can do other things. Name the prim after what it should do, and write what it needs in its description.

Prim name What a click does Description
apply Applies a texture set. The texture set's name.
sendobject Gives an object from the HUD's contents. The object's name.
url Asks the customer to open a web page. The URL.
slurl Opens the map at a location. The SLURL.
group Sends your group's link to the customer's local chat. The group's UUID.
rotate Turns the HUD to show another side. The rotation. See Rotate HUD.
detach Takes the HUD off. Nothing.
finish Lets customers delete the EasyTextures script from their object. Nothing.

Example: give your mainstore's landmark

This button is named sendobject, and its description is Kynno Mainstore. A click gives the customer the Kynno Mainstore object from the HUD's contents.

A sendobject button
The button's name and description
The Kynno Mainstore object in the HUD's contents