The right hand is used to play the strings by plucking them with a pick. A pick is a piece of plastic shaped like a triangle.
Hold the pick lightly between your thumb and first finger, as shown in the photo.
Use the tip of the pick to play the string.
The correct position for your right arm is shown in the following pictures. Notice that your forearm rests on the upper edge of the guitar, just below the elbow. Be careful not to have your elbow hanging over the face of the guitar, or your right hand too far along the fretboard. Also when you are playing single notes, support your right hand by placing the second and third fingers on the body of the guitar.
If you are playing an acoustic guitar, pick the strings over the sound hole as this makes the best sound.
If you are playing an electric guitar, pick the strings between the pick-ups.
If you are strumming a chord, do not support your right hand with your fingers on the body of the guitar but still rest your forearm on the upper edge of the guitar.