Something brief is short and to the point. If you make a brief visit, you don't stay long. If you make a brief statement, you use few words. If you wear brief shorts, you are showing a little too much leg.
As a noun, a brief is a condensed summary or abstract, especially a legal summary of a case. Lawyers submit pretrial briefs to the court outlining the witnesses for the prosecution or defense. As a verb, brief means to give essential information to someone — like the President gets briefed on important matters.