How do you sew on a button that has fallen off a shirt?

Use the sme color string as the other buttons. Now, look at the other buttons on the shirt, are the dtrings inside the button holes cris-crossed like an x, or are they straightup and down like two parallel lines? Follow that pattern, but start underneath the button so the extra string doesn't show in top. Sew 10 times in each directions and the tie a knot underneath when finished.