It is usually used to clean up the asshole more clearly(in particular not the out side of anal but the inside). First you pierce a toilet paper with your finger to the bottom. Second you wipe off your asshole inside but you don't have to be afraid of some feces on the finger. Third you must use another hand and enfold the paper to make it lie on the finger with shit. Forth you give a wipe to the finger pulling out through the hole.
AH1: Hm, your finger smells bad. Did you stick your finger in the ass???
AH2: No. I just made the shit finger.
AH3: Ah, thats ok then.