For starters, there are sites that allow you to trade bitcoin for fiat money. Signing up for these exchanges generally necessitates a slew of additional pieces of identification.
They also have a much smaller selection of digital currencies. You'll find Bitcoin, Ether, Litecoin, and a few other cryptocurrencies on these exchanges, but don't expect to locate obscure small-cap projects.
The second sort of cryptocurrency trading platform is one that does not accept fiat deposits. These cryptocurrency-only exchanges often provide a wide range of digital assets, many of which you may not be familiar with.
Furthermore, these bitcoin trading sites will generally just require a few kinds of identification. Some of them don't even inquire!