When you first invoke Latex-Suite, it scans the $VIM/ftplugin/latex-suite/packages directory for package script files and creates a menu from all the files found there. This menu is created under TeX-Suite > Packages > Supported. This menu contains a list of packages "supported" by Latex-Suite. When you choose one of the packages from this menu (for example the amsmath package), then a line of the form

\usepackage[<++>]{amsmath}<++>

will be inserted into the current file.

The \usepackage line can also be inserted in an easy manner in the current file by pressing <F5> while in the preamble of the current document. This will set up a prompt from the supported packages and ask you to choose from one of them. If you do not find the package you want to insert in the list, you can type in a package-name and it will use that. Pressing <F5> in the preamble on a line containing a single word will construct a \usepackage line from that word.

You can also use the TPackage to insert the \usepackage line.

Once you have inserted a \usepackage line, for supported packages, you can use the Options and Commands menus described in the next section.