Got my first Mac

My sister gave me her old macbook. Pretty sure it's a 2010. I have it running Mountain Lion now and it seems to be handling it well enough. 2 gigs of ram and a core duo. I dunno. The steam client is buggy as hell, that's if it even runs at all, but gestures are neat and I have iTunes Match (or iTunes in the cloud? or iCloud?? wtf???) so the transition from PC was like Steve Jobs' favorite recurring wet dream. Anyway, as a first time Mac user (not that I've never used a Mac before, but that I am a first time Mac User) I'm sure there's a ton of stuff I don't know, and I don't know what I don't know. You guys do. So

Apps, keyboard commands, systemic quirks, anecdotes, animated gifs, all are welcome.

I want you to hit me as hard as you can.