Hi. I've got the instructions here because I have the CD version, so I might be able to help a bit here.

Grabbing hand icon:

Unlike most adventure games, you're not supposed to grab everything with the grabbing hand icon. It's for the treasure hunt/cryptic word puzzle portion of the game - Stauf gives you a hint such as "Winter Coat Worn for a Mixer" and you have to click on the correct object which is somewhere in the house. When you grab the wrong thing you get the voice taunting you for being wrong. When you grab the right thing you get a movie clip and the clue for the next object in the treasure hunt. If the cryptic clues are stumping you, you can get more detailed clues to the treasure hunt each time you click "Help" from the top menu when not in a puzzle.

As for volume controls, assuming the GOG version is the same as the CD version:

Volume Control:

Up arrow/Down arrow increase and decrease general audio volume

Audio Balance:

Right Arrow increases voice level and decreases music level, and Left arrow does the opposite.

From memory, I think the eye icon is supposed to indicate something you can get a closeup of (often but not always a puzzle) and the brain icon should be to actually do a puzzle.

Hope this info helps. I like this game despite its flaws.

It's amazing what nuggets of info one can derive from the simple act of reading a game manual...;) Generally, such manuals are good for things like learning how to control volume and other things. Give it a shot...!