Crypto Currency is a name for a number of digital currencies that uses cryptography to secure, control and transfer amounts between people on the Internet.
Bitcoin was the first crypto currency that was launched in the beginning of 2009. And has remained the de-facto crypto currency since the start and during the period that followed. Since Bitcoin was launched over 1600 of different crypto currencies have been launched. All the other crypto currencies besides Bitcoin have often been refered to as Alt-coins (Alternative Coins).
Most of these Alt-coins offer few new properties besides what Bitcoin offers. It is often just based on the same code as Bitcoin with some technical aspects tweaked and changed a bit.
A list of the names of some of the cryptocurrencies
Some of these cryptocurrencies have been created as a result of a "fork". A fork happens at some point in time when at a specific block, the blockchain splits and creates two chains and two currencies. This can happen when a fraction of the developers wants to change something that is not compatible with the current version and then creates their own client that does the split. Anyone is free to create a fork, but the market will decide if the new fork has any merit.
It is relatively easy to create a new crypto coin. But if it will be successful depends on how well it is received. A new coin without any technical innovations or special purpose will be useless. A pump and dump is common that a new coin gets pushed out with a lot of hype then quickly gets dumped.
A common naming scheme for a new crypto coin is to call it something similar to Bitcoin to try to make it the new official Bitcoin. For example Bitcoin Cash, Bitcoin SV, Bitcoin Gold and Bitcoiin.
For the few most liquid crypto currencies it is possible to trade them in a number of ways. For example on special Internet crypto exchanges. Also some Forex brokers offer ETF-like products for some of the most liquid crypto currencies.
Most of these exotic crypto currencies only trade on Internet crypto exchanges. Some of these exotic crypto currencies don't trade at all, and some are more or less failed projects.