Have a look at this fantastic website that has examples of the sounds instruments make in an orchestra. Vital listening.
Now if you skip through to 2 mins into this video, you will see a violin (Nigel Kennedy playing) and a cello on their own. They are playing some Bach inventions, but it is a great way to hear the difference in sound and see what the instruments look like and how they are played. They are both string instruments.
So, here are the main string instruments. Violin, Viola and ‘Cello. There is also the double bass, but not in this extract.
This film features pizzicato (plucking), tremolo (that suspense effect) and arco (with the bow). Oh, and homophonic music, imitation and much more.