Your personal Tumblr journey starts here
To Boop - either tap the boop button next to someone's name or go to their blog and tap the cat paw icon
To Super Boop - go to someone's blog and hold the cat paw icon until it spins once, then let go
To Evil Boop - go to someone's blog and hold the cat paw icon until it spins twice, then let go
Can't Boop - either you or the person you're trying to Boop hasn't opted in yet
To Opt In - go to your feed and you'll see the boop-o-meter and the option to opt in
I'll update this when I know how to get certain badges and such.