Some things I take for granted in windows (like renaming a folder I've created) I can't find the option for 
Just hit enter on your folder or file and type in a new name. It wont open said file / folder like windows does. 
yeh you need to press CMD and O to open stuff.
I transitioned from MS-DOS to Windows to OS X and the transition can be quite jarring from Windows to OS X and it took me around 2 weeks to fully understand what the heck was going on. Lots of google searches like "how do you uninstall programs in OSX" and "Why can I only resize OS X windows by dragging the bottom right hand corner"
Once you get used to the interface it's usable.