To access your Group menu, you need to be on the Nodes or content view for your Group. The last tab is Group Menus. Click that and then click the link in the ID column, which should be the name of your Group. This will take you to a viewing of the menu that appears on the left side of your pages.
To add a new item to the menu, click Add Link. The Title should be either the title of the page you are linking to or, if it is a long title, perhaps a shortened version. In the Link field, start typing the title of the page you are linking to and when it appears in the list below the field, select it. If you can't find it in that manner, go to the page in another window or tab and select everything in the URL after www.stlawu.edu and copy it. Then go back to where you were creating the new menu item and paste it.
Click save and you will be taken back to your list of menu items. The new one will be at the bottom. Use the arrows to the left of the item to position the new link where you want it in the menu. Move your cursor over the arrows next to that item, click and hold your left mouse button and drag the item to where you want it, then release your mouse button. If the item should be a sub-menu of an existing item, you can ident it by dragging the arrows to the right.