Every major crypto exchange offers Bitcoin trading pairs. Example: Ether/Bitcoin, Litecoin/Bitcoin and so on and on. Some of the exchanges like Bitrex allows you to trade Crypto for USDT  (USDT is a crypto currency allegedly pegged to the US Dollar.

Some of the exchanges allows you to trade Fiat to crypto such as Coinbase, CEX-IO and others.Some of the Altcoins have out performed Bitcoin on a short therm or during specific periods. But there is no coin that has performed consistently as Bitcoin. Most of the major Altcoins follow the same trend.
Bitcoin is the King and Queen and all the Altcoin are at best following it. Bitcoin is the number one coin and, so Bitcoin decides the market price in General. And this would imply that all other altcoins are kind of pointless. And we all know it is not true, because some of the Altcoin have a great technology such as Ethereum smart contracts.