Get used to those freezes when trying to catch a pokémon!
That's a stupidly common bug (largely due to the overloaded servers failing to respond in a timely manner), and the only resolution is to force quit the app, relauch, and hope for the best. Sometimes you win; sometimes you lose.
And don't think you missed some instruction about the pokéstops. You didn't. The built-in tutorial is garbage.
12K steps? Awesome!
I've seen this reposted from a dozen different "sources" over the last few days:
Same thing surely goes for us big kids.