It is thought that there are about 200 sign languages around the world. However, you can probably never arrive at an exact figure because sign languages change and merge with others just as spoken ones do, but faster. As well as the officially known languages, there are countless small or local systems of signing which groups of people come up with to meet a particular situation - for example within a family or small community where nobody knows any of the official sign languages, but there are one or more deaf people.
One of the best known official languages is American Sign Language (ASL), which is used in most of North America along with Mexican Sign Language. Another well known one is British Sign Language or BSL; surprisingly to many people, although US and UK English are basically the same language, ASL and BSL are not.
Besides the different sign languages used in different countries, there is a system called finger spelling, which is used along with sign languages. Most sign languages have some form of finger spelling.