Well it's kind of hard to explain Tumblr, but it's basically a place where people have their own "blogs". Most of it isn't considered actual blogging though, we just "Follow" people who blog about stuff we like and share posts. Some people say it's kind of like Facebook, but better.
You can use these instructions for starting up an account:
link
(Just in case you make one, my username is "Trollzusa". x3)
