By now you should be able to play notes with confidence.  A chord, is more than 1 note played at once.  These are slightly harder, and can be frustrating at first.  Below are the 7 regular chords

A

B

C

D

E

F

G

Try and practice moving between chords and adding extra notes with your spare finger.  A quick hand to chords is an easy way to write songs and learn other pieces.  All the notes in a chord will match one another when played on their own.

A,C,D,G are all major chords and sound "happy"