Currently there are some known issues with the Rich Text Editor(RTE). You cannot enter HTML in the RTE as it becomes plain text instead of code. If you want html tags to actually be parsed you need to enter them in plain text mode.
Also any HTML code you enter in the plain text mode will be erased if you switch to RTE before saving. There is currently a lot of discussion happening here regarding the RTE and its abilities, we're working on making it more useful and less finicky.