0 DESIGN GOALS
The properties you would like yuor system to have: distributed, decentralized, immutable, etc.

1 IMPLEMENTATION
You choose to implement those properties in a certain way to create an implementation.
– Open: BTC and ETH are BC implementations,
– Permissioned: Hyperledger Fabric, etc.

2 INSTANCES
Once you have decided on your properties and decided on a protocol to implement those properties then you create as many instances for your implementation as you want: different networks to create different ledgers or version of reality.