If I want to use the marginpar command, how to control its position? Namely, the marginnote appear either on the left or on the right. And I want to control the width of the box and the innersep inside the box, as well as the distance L of the box and the edge of the paper. Sometimes the distance L is negative. In the following picture, L is out of the edge. And if I want to pan up the note distance S, what is the comment? Notice here we set the command only for a particular paragraph, not setting for the whole document.
\documentclass{amsart} \usepackage{lipsum} \begin{document} \lipsum[1]\marginpar{ABCDEFGHIJKLMNOPQRSTUVWXYZ} \end{document} 

geometrypackage?\marginparwidth. But maybe you should consider using themarginnotepackage, that gives you more options to customize your margins.