The simplest answer will be, You have Ethereum platform with its own blockchain and coin named Ethereum(ETH) which can be mined, and you have various ERC20 tokens, which are built on Ethereum platform, uses Ethereum blockchain and wallet for transactions. A coin is basically built on its own blockchain, with its own wallet, whereas token is built on another platform like Ethereum, Waves, EOS etc. A token will use the platform's blockchain and their wallet address to facilitate transactions.