Shower is falling apart. Now what do I do?

basic tiles cost about 14 cents a piece at Lowe's ,if you just want to fix it temporary just use anything 1/2 thick sheet rock , plywood ,most of what you see is the paper rotted off the gypsum maybe you can scrap it down abit and then use thin-set on and apply the same tiles cleaned up or new ones for a temporary fix ,if it's temporary just use the thin-set as grout fill the cracks and wipe off excess with cloth rag