You need to click inside the area you want to start typing, so that the flashing cursor appears.

Before you do this you have to wait for the top line to load - that's the line immediately opposite where it says 'comment:'

Once you've done those two things change the text to 'arial' for example and start typing.

Alternatively onece you've typed your message - highlight all the text (like you learnt last time) and click on the top line - B for bold, or change the font type or size.  Have a go its fun.