Hm. I’m a little pressed for time, so I can’t do a full step-by-step; there are however several on the Internet with a quick Google search: illustrator layer mask tutorial
Basically, you will:
1) Create a background fill that is larger than all the outlines of the letters (a rectangle is fine).
2) Create the shapes you want to overlay the background and give them the appearances you want. Be certain that any design elements you don’t want seen are outside the outlines of the letters.
3a) It helps if you have combined all the outlines of the letters into a compound path (CTRL-8)
3b) Group all of the elements you just created with the text outlines.
3c) In the layers panel, move the text outlines to the top spot in the group.
4) Turn the group into a clip group. (In the layers panel, the light & dark boxes icon right next to the hour glass, or one of the other ways described in the tutorials you find in the search.)
You should be done. Just tweak your design to your needs.
Steve Crook, Jr.
http://www.stevecrookjr.me
I am a simple creative professional that can get my Adobe suite and a few other creative tools to do what I want. Barely. 🙂