[ceptimus]

Go for a common distro of Linux so that it's easier to find help on line. Maybe Ubuntu but there are other good candidates.

Expect to use a terminal (like the Windows Command Prompt) more often than with Windows or Mac. Depending on what you're doing it's not strictly necessary, but it's often easier than doing the same things from the GUI - if and when you run into problems or want to set your PC up to do something slightly tricky, you'll find that most on-line solutions will involve typing stuff into a terminal (aka shell or console). It's worth learning some common terminal commands like cd; ls -l; df -h; cp; mv; also the (confusing at first) layout of linux directories (folders) and linux file permissions and the ways of altering them (chmod; chown).

You'll pick it up a bit at a time. Noobs often say how confusing things are - of course it's probably less confusing than all the arcane stuff they've already learned about Windows with things like the Control Panel, Device Manager, System and System32 folders and so on - but they already know that stuff so they claim it's 'obvious'.