The GAS token is a type of currency used to pay computation fees on the Neo network. It fuels the network by being the required gas for transactions and smart contract executions. BTS also has its token, comparable to GAS tokens, which is called "BTS Gas." The NEO token is another type of currency introduced to Neo after Ethereum ran stable for a while. The NEO token does not have any function other than deciding how changes are implemented to the network. For example, if someone wanted to propose a change to have a new feature on Ethereum, they would need at least 51% of the community's support, or else they would reject the proposal.