A cellist holds their instrument between their knees. It is propped up on an adjustable endpin that rests on the floor. The cello is played by drawing the bow across the strings with the right hand; the bow causes the strings to vibrate. The hollow wood body of the cello amplifies these vibrations, producing sound. The player changes pitch by depressing strings with his or her left hand.
The strings of the cello are tuned to the pitches C-G-D-A. C is the lowest string.
The easiest way to check that a cello is in tune is with a digital tuner. Most models produce a drone pitch for tuning by ear. These tuners also have a display that indicates whether the string is sharp, flat, or in tune. If you don't have a digital tuner with you, you can use a pitch pipe, piano, or virtually any other instrument to produce the pitches you need. Some players prefer to use a tuning fork. An A-440 tuning fork produces the pitch for the A string. From that reference point, the player tunes each of the other strings by tuning the perfect fifth intervals.
Once you have the tuning device in place, you can adjust the pitch of your instrument by turning the pegs the strings are wrapped around. Tightening the string raises the pitch; loosening the string lowers the pitch. Many cellos also have fine-tuners mounted on each string near the tailpiece. The player can use a fine tuner to adjust the string even more precisely by turning the small screw.