How to make your font size bigger

above the post box (where you type your message) there are various buttons and drop down menus that produce what are called 'tags' in HTML. At the end of every part that you want to make larger (or change the colour or font) you need to press the 'close all tags' button to make it work. So you should have something like this:

(SIZE=7) Hello everyone (/SIZE)

except the brackets will be square.

Hope this helps!