The Abdim is a little tough because it has a muted string right in the middle. Start by placing your index finger on the first fret of the G string. Next the middle finger goes on the second fret of the C string and the ring finger plays the second fret of the A string. Here you don’t want to keep your middle finger straight up, let it lightly touch the E string so that it mutes it. Pluck all the strings to be sure the right notes sound and the dead string stays silent. If that E string is played the chord will not be the same.