Layer 1 blockchains are standalone networks with their own consensus and native coin: Bitcoin, Ethereum, Solana, Cardano, Avalanche and others. They secure themselves and keep the transaction history, and applications and layer-2 networks are built on top of them.
The native coin usually pays fees and is used for staking or mining. The networks differ mainly in speed, transaction cost, decentralization and the size of their app ecosystems.