I think only subscribers can recommend posts. Look for a link 'recommend' underneath each post. Do you see it? If not, I guess I am right then.
The idea is that useful, interesting, funny, etc. posts get recommended. And by looking at the recommended posts you can then easily find those interesting post (and thereby the threads they are in. However, a lot of garbage also gets recommended.
So ignore the "It's called a penis" posts (if you don't find it funny) and read the ones you find interesting instead.