It's different from FB in that you don't "friend" people, you follow them. When someone you follow posts (tweets) you see it in your continual feed. I use Twitter more for news outlets and other organizations that are of interest to me (psychology, health, science, and technology-based information). Other people use Twitter to follow their favorite musicians or movie stars or politicians. A tweet can be just a comment, but the places/people I follow typically include a link to an article that I can read.
I use Twitter for another "news feed" source, but it can be used much like Facebook to communicate with friends and family and to link to pictures and other things. I just find uploading pictures to FB to be easier. I also use FB to communicate with my group of women friends in a private group. I don't know how to do that with Twitter, it seems that everything tweeted is seen by everyone who is following you, and there's not an option that I know of to tweet to just a certain group.