I always thought how do people use Bold or underline in Facebook chat. Well here is how to do that.
When you are chatting with some one on Facebook chat you just need to add some symbols to make your text as required. If you want to write an underlined message add underscore before and after the word.
Eg. _Text_
If you wish to write a Bold word then use asterix before and after the word.
Eg. *Text*
To use bold fonts type your message between two asterisks.
e.g. *message*
Try this and let me know if you find this good. 
If you know any other such tricks do share with me.
ayush
ayush kumar