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Pressing Esc will take you to the main menu where you can configure most controls. If your mouse has a scrollwheel, be sure to use it to zoom out a bit too — this resets after every load game though. Most players find it easier just to use the keyboard though.

If you are having trouble picking up an item press (the use key) left Ctrl+↑ to pick it up. Transferring items from chests etc…is usually Ctrl+→.

Have a fiddle with the settings in the game and get a feel for whatever works for you. Jump only works when either moving and pressing jump or if you are standing against a wall/cliff and press ↑ at the same time. If the slope is less than (say) 80°, you may not be able to grab it even if it looks like it'd be a cakewalk.