Ah, sorry you're having trouble, here's a quick little tutorial:
-Click anywhere to advance text.
-Click on anything that has action-text to interact with it (e.g. the doorknob, the drawer or the little plug on the bed).
-When the player's butt-interface appears, click and drag them to interact. The goal is to get them stretched out over whatever insert-able object you found.
-Find something that's just big enough to improve your stretching ability. This lets you stretch out over even bigger things!
-Make sure you don't miss anything! Hover over everything to see whether you can interact with it or not.
I don't want to spoil any of the puzzles from there, but some nice people have left some clues and tips in the comments for some of the later-game stuff.