Coding Assistance.

Hello! I've returned after a long time away and just getting back into the swing of things. Now, coding when posting a thread...how does it work? I can find the MyCode Reference but when I try to incorperate those into the  thread, it shows on the preview, but not on the post. It just shows the bracketed code with no changes. Is there a setting I'm supposed to be in? I just want to change the text size, mostly. 

Thank you!