Bridges are what allow agEUR and the ANGLE token to be available on different chains. Since agEUR (and ANGLE) only exists natively on Ethereum mainnet, the bridges for agEUR (and ANGLE) all do the same thing: they lock agEUR (or ANGLE) in a smart contract on ETH side, and mint new tokens on the corresponding chain. When bridging back agEUR (or ANGLE) from the corresponding chain, tokens are burnt there and released from the smart contract on Ethereum mainnet.