I'm installing the Schluter Kerdi membrane in the shower. It bridges from the fiber-reinforced cement wallboard, to the back concrete wall, and between both those and the poured-in concrete shower pan.
The general technique is: smear especially viscous thin-set mortar on the wall, back-scrape it with a notched trowel, then set the membrane on top and rub it into place, smooshing the underlying thinset about so it bonds to the whole surface of the membrane.
Here's an important hint: the kerdi comes in rolls, so it has a springy closure action to it. One by-product of this is you better make sure you have the membrane oriented so it wants to roll into the wall, rather than off the wall, because it will do exactly that. The tips all come off the thin-set and you have to stack wax-paper-encased boxes against it to keep it in place.
Folds in corners are really difficult. I don't know how to do them. I should've purchased some of the pre-made corners, but my brother assured me that it was easy to do.