A parbox is a box whose contents are created in paragraph mode. The \parbox has two mandatory arguments:
1. width: specifies the width of the parbox; and
2. text: the text that goes inside the parbox.
LaTeX will position a parbox so its center lines up with the center of the text line. An optional first argument, position, allows you to line up either the top or bottom line in the parbox.
A \parbox command is used for a parbox containing a small piece of text, with nothing fancy inside. In particular, you shouldn't use any of the paragraph-making environments inside a \parbox argument. For larger pieces of text, including ones containing a paragraph-making environment, you should use a minipage environment.