A pick is a drop-shaped piece of plastic. You hold the pick between the tip of the right hands index finger and thumb. It is available in various thicknesses. Try to start out with a pick 1.5 mm. thick.
If you need to play slowly or powerful, only use down-strokes. Use alternating down and up strokes if you need to play fast. Let the outside of your hand rest a bit on the bridge while playing. The pictures show how to hold a pick.