How do I view someones profile?

If you've sent or received messages with the person, go to the messages page and view the conversation. Then click their photo or name that shows up at the top of the conversation to view their profile.

If you're viewing a post, the profile of the person who posted will show up below the body of the post.

And when you're viewing the profile, you can click on the persons photo or name to view all their past posts.