Congratulations! After you learn the D7 guitar chord you have learned the fifteen most commonly used basic guitar chords.
The chord diagram on the left is for right handed players, and, the diagram on the right is for left handed guitarists.
The D7 chord uses four strings. Strum it slowly, up and down, as with the other chords. Spend some time switching between the D, Dm, and D7.
Switch between all the chords you know, and spend extra time on your weak areas. Practice until you can switch quickly.
When you learn a new song, there may be a new chord or two that you don't know, but, most songs will only use chords you've learned here.
Learn any new chords the way you learned the basic guitar chords, and practice switching between them and the other chords in the song.
Lets go over some chord change tips:
Have some fun strumming along with your favorite songs. Get your hands on some song books, guitar magazines, or online tab, and play along with the music.
If you lose your place in the song, keep it playing and catch up. Stopping part way through, then starting over is a bad habit to get into. You can stop and start to learn sections of a song, but, when you are performing the whole song (even alone), catch up to where you are supposed to be.