You will need 2 Mallows (any generation) in order to breed a new Mallow.
The DNA of each Mallow is saved into the blockchain. When you put mum and dad together for a breeding session, baby mallow is generated based on a random mix of their DNA.
For Gen 0 Mallows freshly minted from design studio, you will need to wait 24 hours to breed 1 baby Mallow for free. Or you can just go on to keep breeding at 1 MTRG for each baby Mallow.
Breeding is free every 24 hours, because mum and dad Mallows need their break time too.
If you breed before the 24 hour break time, it will cost 1 MTRG to breed.
When breeding, there may be a few Metamask approvals required.
1) Approval to use your MTRG tokens with the MeterMallows smart contract. (if insufficient approved)
2) Approval to call the breeding method in the MeterMallows smart contract.

Gen 1