ERC20 is a standard or a set of rules for Ethereum based tokens. Tokens that satisfy these set of rules are called ERC20 tokens. These tokens are actually smart contracts on the Ethereum network and have different values. When sending an ERC20 token to another wallet, you will need to have enough ether in your wallet for the necessary transaction fees.
The amount of time for a block to be confirmed varies depending on the token. Fees are calculated according to the complexity of the transaction (gas) and paid in ether.
You can switch between currencies from the Home screen, which is accessible by the back arrow found on the top left of any currency screen.