Bookmarks help you navigate around a large project. You can return to a bookmark in a single jump instead of having to search for the code in a long file.
Use Toggle Bookmark to set or clear a bookmark - the line will be marked by a cyan box in the margin. You can have as many bookmarks as you want and use the Previous Bookmark and Next Bookmark buttons to move between them. If the file holding the next bookmark is not visible then VB will open a new edit window automatically.
The Bookmarks commands are on the Edit menu but they're easier to use from the Edit toolbar. Select Toolbars from the View menu if this isn't visible:
Don't confuse these editing Bookmarks with Bookmarks in RDO, in HTML or Help files, or in DataGrid controls.