CSPR is the native token to the Casper network. As a Proof of Stake blockchain, Casper relies on CSPR to reward the validators that participate in the PoS consensus mechanism to secure and uphold the network. Casper users pay the fees with CSPR. Validators and governors receive CSPR token as a reward. Casper users also rely on CSPR to pay network fees for on-chain actions. The CSPR token was available through CoinList for the initial public token sales (March 23-28th, April 7th, 2021). One can nowadays purchase tokens on certain trading platforms.
All future tokens will only be those created algorithmically to reward validators. This will be a single digit percentage inflation each year, much like in the Ethereum network.
To take part in the DPoS process, users save up digital assets to form a 'stake,' and delegate it to those who do all the upkeeping work and get a share of the reward in return. This process is called staking. By staking, you take part in the consensus mechanism.
Staking is a vital process for DPoS blockchains. It allows selecting the best block producers to do the work, ensures decentralization and minimizes the chances to ruin the network. Staking allows more block producers / validators to be involved in the blockchain, and more network users to collect rewards.