Bitcoin is the most commonly known name of cryptocurrency however, people associate that name with all 'digital' currency.
There are plenty of different types of cryptocurrency outside of Bitcoin.
Bitcoin, Ethereum, and Litecoin are highly popular and can be easily purchased through providers such as Coinbase.
Altcoins are the name given to anything outside of Bitcoin.
The coins aim to solve different problems in their own markets.
Many altcoins are worth very little due to the fact they have yet to gain traction in their technologies.