. I hear tumblr is more or less the same (I believe it's an image board?) but it seems more complex, with all the blogging and such.
Tumblr is a "microblogging" social network site. What you're thinking of is 4chan, which is an imageboard. Pretty much there's what's called a "dashboard", that's their equivalent of the newsfeed, where all the posts from people you follow appear. Example from my dashboard.
The main idea behind tumblr is to "reblog" content , or re-post it your blog similar to twiiter's retweet. You can also like posts as well. Both likes and reblogs are a part of what is called "notes" and obviously the more notes a post has , the more attention it gets.
Just felt like clearing that up with you. :) Tumblr honestly isn't bad. There's alot of really funny posts, but also lots of weird people too. Though just a a heads up, you'll run into a good amount of people who pretty much get offended by EVERYTHING and tend to jump to conclusions. (Particularly "feminists" who practically get mad anytime men's rights or men are mentioned. I put feminists in quote cause really, that isn't what feminism is about.)
For example. If you follow the right people though, you really don't find much of those kind of people. I've found some really nice people there.
Tl;DR Tumblr is a microblogging site, 4chan is the imageboard. Tumblr isn't bad and has a lot of funny, nice people, but it also has a good amount of annoying people.