There will be a skippable Tutorial where you can get some experience first how to play the game. For example you test the "Planet Exploration Vehicle" (PEV) on the lunar surface, collect and return rare elements to the Moonbase helping to build your own ship.
You will conduct your first navigation tests within the solar system before you'll receive your promotion to a space ship captain. You can train and specialize a Crew, like in a Role Playing Game. Certain capabilities of these Crewmembers will come in handy later in the game. And then... you will jump into the first extrasolar Star System.
First you will scan the central star and its planets, seeking information. Then you'll go into orbit of one of these Planets. Once you decided where to land, you can disembark and drive around with the Planet Exploration Vehicle (PEV) and collect Ores, explore Ruins and discover clues to the Story or new Technologies.
You will encounter various Alien races and communicate with them, trade or fight which depends on how you talk to them and what characteristics they have. Once you return to the base, you can store the collected Ores, explore the discovered Technologies, rebuild and install them in your Spaceship. The more you explore Planets and talk to Aliens the more you're going to learn about the Universe, its history and the Alien races.
You will be absolutely free in your decisions. You'll get a basic Spaceship, a Main Quest and then it is up to you what's coming next. So you can decide to follow the main Story, achieve a side Quest, explore a tiny little useless Planet or just search for a yet unknown Alien Race.