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 improvement method 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 validator who perform good result will be reward with DOT token, while bad validator may lose some of their token.
3. Bonding: Blockchain that wants to be connected with Relay Chain via bridge has to stake DOT token to the network through the collators.