Polkadot or DOT token is the cryptocurrency of the Polkadot network. It has 3 main functions as follows.
1. Governance: DOT token holders can participate in voting for the improvement of the network.
2. Staking: In order to be a validator within the network, the holders have to stake some of their DOT Token to network in the process called staking. The validators who perform good results will be rewarded with DOT tokens, while the bad validators may lose some of their tokens.
3. Bonding: Blockchain that wants to be connected with Relay Chain via bridge has to stake DOT tokens to the network through the collators.