If you should ever need that stencil again, it's readily available: On the File menu, point to Shapes, and then point to My Shapes. Find the descriptive name you gave the stencil, and then click it.
If someone gives you a stencil file (a .vss or .vsx file), you'll need to copy it to a special location on your hard drive to be able to access the stencil by using the File menu and Shapes submenu. That location is:
C:\Documents and Settings\user_name\My Documents\My Shapes (where user_name is your Windows user name).
Instead of trying to remember this path, you can do the following:
Windows Explorer will open the appropriate folder for you. After the file is copied to that folder, the stencil will be available on the My Shapes submenu.
To draw your own shapes, use the Drawing toolbar.