All that you need are already supplied by egreg in his comment. Fact: You don't need to define these commands anymore.
You also mentioned the \boxed command. Incidentally, you don't have to define this too. This is already provided by the amsmath package. This works only inside math environments, though.
A demonstration.
\documentclass{exam}
\usepackage{amsmath}
\begin{document}
\begin{questions}
\question What is the synonym of \underline{Fun}?
\question What is the antonym of \fbox{old}?
\question Can I use both \verb+\fbox{<>}+ and \verb+\boxed{<>}+ to box words? Perhaps $\boxed{4}$ or \fbox{$4$}?
\end{questions}
\begin{equation*}
\end{equation*}
\end{document}
The output

You can look up most of these commands and many things else by reading The Not So Short Introduction to LaTeX2e or other LaTeX guides.
\underlineand\fbox– egreg Nov 29 '12 at 16:24\questionmacro (Where does that even come from?) do underline/box its full content? If not, is\questionrelated to the actual question?\underlineand\boxedare math mode macros (the latter provided byamsmath). Have some ideas:\documentclass{article}\usepackage[normalem]{ulem}\usepackage{amsmath}\begin{document}\uline{Fun} \fbox{Old} $\underline{\text{Fun}}$ $\boxed{\text{Fun}}$\end{document}– Qrrbrbirlbel Nov 29 '12 at 17:46\questioncommand is given when you use\documentclass{exam}or\questionis a macro inexamdocument class. This macro when used will give the text a numbering order.See in the image example above. What I want to have is a command wherein when used this could automatically underline the text in the argument. Or automatically output the text inside the box. – Kayla Nov 30 '12 at 11:30