Of course we can be friends! n_n;
A forum is a meeting place where ideas and views on a shared subject can be discussed! In this case, you're on a Pokemon forum, so most of the thoughts exchanged will be Pokemon related (unless it's in our Off-Topic sections). A post is the means with which those ideas are shared, so for instance, your introduction thread is a 'post'. It's any way a user interacts with the website. And it is most definitely social media, since you'd be using it to create and share content, as well as social networking!
I hope that answers some of your questions! :)