We do have listed in the bottom of the page what you can and cannot do in each thread. Scroll down below the drag and drop, and on the left side you'll see a list of "Posting Rules".
HTML code is typically turned off on many forums, as mentioned above. But for the most part, anything you need in HTML is available in BB code. We can help you with coding it if the link posted by abt2k15 doesn't cover it.