How is the trombone held?
The trombone is held with both hands. Your left hand should form a gun with your thumb and index finger. After this you will put the left hand over the bar with the bell and your index finger will go over the humps on the mouthpiece. Then the right hand goes on the bar of the actual slide and and you use your index, middle, and thumb to hold this bar. The thumb side with the finger nail should be facing you and the other two fingers should be on the other side. Then you can play the trombone. If this does not help you, this website should help (see related link).