Welcome to our community and forums Werot. To answer your question, most of the "banners" found are made, created or edited by photoshop users within our community. To put on a "banner", you must click your name in the top roght corner when you're logged in. If you want to install a "banner" you have in mind. Head on over to the General Discussion section of our forums, there you will find a post named the "Markdown Sheet", up in the stickied front page of the General Discussion. If you need anymore help please do ask it here or at our IRC or Discord. See you around Werot, God bless you.
-MX.