A chord is a group of notes which are played together. Chords are used to accompany the melody of a song. Chords are usually played with the left hand and the melody is played with the right. The first chord you will learn is C major, usually just called the C chord.
The C chord contains three notes - C, E and G. To play the C chord use the first, third and fifth fingers of your left hand, as shown in the C chord diagram.