Bookmarks are your reference to a segment of text or a line inside the Kile environment. To use a bookmark, select a specific line of your document you would like to return to, then press Ctrl-B, and Kile will add a bookmark to this line. Alternatively, you can also set a bookmark by highlighting a line and choosing the menu labeled Bookmark->Toggle Bookmark.

To remove all your bookmarks, select Bookmarks->Clear Bookmarks.