Conducting
Conductors usually beat time with their right hand.  This leaves their left hand free to show the various instruments when they come in (when they start playing) and to give interpretative gestures, such as indicating when to play louder or softer, or faster or slower.  Most conductors have a stick called a “baton”.  It makes it easier for people at the back of large orchestras or choirs to see the beat.  Other conductors, such as those who lead singers, prefer not to use a baton.  A conductor stands on a small platform called a “rostrum”.