The bookmarks feature allows you to mark certain lines, to be able to easily find them again.
You can set or remove a bookmark in a line in two ways:
Move the insertion cursor to the line and activate the → (Ctrl+B) command.
Click in the Icon Border next to the line.
Bookmarks are available in the menu. The individual bookmarks are available as menu items, labeled with the line number of the line with the bookmark, and the first few characters of the text in the line. To move the insertion cursor to the beginning of a bookmarked line, open the menu and select the bookmark.
To quickly move between bookmarks or to the next/previous bookmark, use the → (Alt+PgDown) or → (Alt+PgUp) commands.