Do you know where it is described?
https://ethereum.org/en/eth2/staking/
https://launchpad.ethereum.org/overview/
Picking any active validator on the Beacon Chain, we can see that there is an Eth1 deposit and a corresponding Eth2 deposit:
https://beaconcha.in/validator/91676#deposits
https://beaconscan.com/validator/91676#deposits
If you're interested in the technical details, see:
https://github.com/ethereum/eth2.0-specs/tree/dev/specs/phas...
Do you know where it is described?