You should see a "Download Latest Software" link on the main page of Hake.me you can click on and start the process, it's a pretty simple process if you've downloaded any sort of .exe program before.
If you've never downloaded any .exe type of program before in your life which I find hard to believe lol, then there are step-by-step directions here https://hake.me/docs/getting-started/ that will guide you through the process.
No real person on here should ask you for a username and password. The Hake program itself you downloaded is probably asking what's your Username and Password on this forum so it can log you into the Hake client you just downloaded.
nope, you just download the software start it with the option suiting you, when you enter the game with the default key insert you open up a menu and find whats necessary there.