Key in or play in your melody. Open the Score window. Click the 'A' part-button from the buttons right below the toolbox. Right below that you'll now see a.o. a 'lyrics' partbox-object. Drag the 'lyrics' object to right below the note where you want your lyrics to start (the top of the window where normally the menubar is will turn blue-green and have the text "insert lyric"). Type in the lyrics: hit tab (and not return) to move from one note to the next