*bold* should get you bold (outside of math mode). Gavin is correct that things like \bf and \textbf are used in TeX mathematics mode. So how you do it depends on whether you are in math or not.It is best if you post a complete example of what you are trying to do (not just an isolated snippet as you have done), so that we can see the context in which you are working. It is also helpful to say what is happening. A phrase like "it's not working" is not very descriptive -- does this mean the text doesn't show at all? That it isn't in bold? That you get an error message instead of text?
The more detail you can give about what you expect versus what you see, the better.