Highlight the text you want to underline (left click and drag curser over the text) and select the tab 'underline' from the tabs above. Select 'Go Advance' tab below to do more things with your text.
Underline is the (u)(/u) tag and strike through is (s)(/s). Another fun one is (inv)(/inv) which ʇxǝʇ sʇɹǝʌuı. Replace the ()'s with []'s.
