How can I make a semi-transparent box in my android app?

How can I make a semi-transparent box in my android app?

Here's an example:
https://lh3.ggpht.com/G_l_bfH1SzWjSYn8deZ73AqoBMpoVSPDfoOqawkSAh83h7QcGnLE9C8HVuiERZYGEg=h900-rw
I want to add buttons in this box, just like app above.