You can quickly jump to any bookmark by pressing Ctrl+1, Ctrl+2, Ctrl+3, etc... on the keyboard. Jumping to a bookmark positions the text cursor on the line on which you set the bookmark with the given number through Mark|Set Bookmark. If the requested bookmark does not exist, nothing happens.
If you remember you set a bookmark but don't remember which number, open the Mark menu. The 10 Go to Bookmark X items in the menu will display the first few words on the line on which each of the bookmarks is set.
Bookmarks can be either separate for each file, or project-wide. When bookmarks are project-wide, the Go to Bookmark command searches for the bookmark in all files in the active project. If the bookmark is found in another file, it will activate that file. When bookmarks are separate for each file, the Go to Bookmark command will never switch to another file.