Bitcoin is the most famous Crypto Currency coin and currently still has the top market share and biggest market cap among all coins.
Yet there are many different coins with different purposes is mind. Some coins have been created for smaller payments, some for fast payments and some for privacy. Others have nothing to do with payments and are intended as utility tokens or for smart contracts.
The best place to see all current coins, their market cap, volume and history has been for a long time CoinMarketCap. But recently, there have been reports of manipulation and other sites have popped up, which offer the same, if not more, information, like CoinGecko or OnChainFX.
These sites are also the ideal place to start researching a coin, check out its website, developers and use-case. And if you want to trade the coin, you can also see the exchanges that list the coin for trading.