How to make sprite alpha transparent

Hello, I am trying to figure out is it possible to make a sprite tranparent in the 2d world. I am making a message box semi transparent on my 2d game. I will appreciate any help..

also this will be my first time dealing with 3d features of blitz could you post any examples you can??

A simple way would be:

Sp = CreateSprite()
EntityAlpha Sp, 0.5 ; (Alpha Transparency 0 - 1)