As a long time Windows users I'm used to switch between two windows using keyboard. Now at Mac I just can't figure out how to do that!
Command-Tab works nicely between apps, but how to do the same within one application having several windows open? Especially when using XCode? For example within Firefox you can do control-tab and control-shift-tab to navigate between tabs. Doesn't work with XCode, not between two different open projects.
Doing 4-fingers-down, looking at screen, finding the previous window and clicking on it with mouse takes waaaay too long time. It interrupts whatever I was doing, distracts from whatever I was thinking about and starts annoying me - enough to write this desperate call for help in StackOverflow :)
There's got to be a secret handsha... keyboard combination!