Coins are assets that they have their own blockchain. Tokens are smart contracts (programs) that exist on another blockchain. Care must be taken, when you invest in tokens. To pay the transaction fee you must have coins of the underlying blockchain. To make it simple, when you have an ERC-20 token (token using ethereum blockchain), you must have ether to pay the transaction fees for any action with the token. It is advisable to choose a blockchain that you like, and trade tokens there. This eliminates the need to have different coins, to do transaction fees. It's better to stick with one.