NEO is China's first open source blockchain. Imagine NEO as a share of a company. As a shareholder of NEO you will get involved in important decisions
and will receive regular dividends. There exists a total amount of 100,000,000 NEO representing all of the ownership of the NEO's blockchain. NEO are currently available on the market. The remaining NEO are held by the founders and distributed regularly to support future projects built on the NEO blockchain.
GAS are the dividends for the shareholders and run the blockchain like Ethereum's GAS. With every new block GAS is created and proportionally distributed to all NEO shareholders.
The creation of GAS will reduce with every 2,000,000th block. With the 44,000,000th block the last one (1) GAS will fullfill the total amount of 100,000,000 GAS.
To get in depth information about Neo and GAS see the official whitepaper.
To calculate your future GAS earnings see the neodepot.org calculator.