What is no man's sky?
No mans sky is a procedurally generated space game. It has 18,000,000,000,000 planets which are all unique and procedurally generated. The animals on the planets, space ships (driven by npc's and ones you can buy) and even the geography and chemical make up of the planets are all procedurally generated meaning there is a huge variety in almost everything you will encounter in the game. You can play as a trader, explorer, fighter or as a combination of the above.
You can earn credits by trading (buy low in one system, sell high in another), discovering new animal types and uploading them, fighting (as a pirate or defending cargo ships against pirates) or even mining resources from plants and selling them at a space station.
When you first start the game you will find yourself on a planet at the edge of the galaxy with a low level ship. A goal a lot of people will probably set themselves will be to reach the centre of the galaxy as no one knows what is there. However this will not be easy as the galaxy is life size (hundreds of lighters across), luckily space ships equipped with hyper drives can "jumps" to other solar systems, the best hyper drives are extremely expensive so you will need to make money to afford them. As you travel closer to the centre of the galaxy it will become harder to survive so expensive weapons and armour upgrades are needed but trading, exploring and fighting also become more profitable. Robots called sentinels patrol some planets to make sure nobody mines too much or kills the wildlife.