Kusama provides a way close to the real environment to test the Polkadot network in advance to ensure the security of the Polkadot network. It also allows future Polkadot network participants to practice in advance, such as validator nodes, parachain teams, and builders of Polkadot ecological tools can use Kusama to prepare in advance.
KSM is the native utility token of the Kusama network. Its main functions include:
Governance: KSM token holders can vote on network governance.
Equity Consensus Mortgage: Relay Chain network validators need to mortgage KSM tokens to run nodes.
Join the network pledge: Parachains need to pledge a certain amount of KSM tokens when joining the network.
Handling fee: KSM is used to pay the handling fee generated by cross-chain information transmission.

Kusama is a public chain set up for major experiments in the Polkadot network.
A major difference between Kusama and Polkadot is that Kusama adjusts network governance parameters to allow faster evolution of the network. For example, the voting period is 7 days and the implementation period is 8 days after voting.
Kusama's infrastructure includes Relay Chain, Parachains, and Bridges.
Relay Chain is the main blockchain of Kusama network, and all Kusama nodes run on Relay Chain.
Parachains are parallel blockchains connected to Relay Chain, maintained by their own network validators, Collators.
Bridges are special blockchains that connect Parachains with external networks such as Bitcoin and Ethereum.