It's important to remember that this is a supplement to dungeons and dragons 5th edition, so the gameplay loop remains largely the same. Players can create their characters (known as agents) like they could before, progressing and developing those characters as they did before by earning experience as they go along. The only difference now is that they will be choosing from a mixture of alien races, modern classes, and futuristic backgrounds. Out of the box Atlas Moment offers converted versions of all of the core fundamental options found in the player handbook, but moderately adapted to suit an science fiction setting. It's not entirely necessary that players know what aspects are converted from what, but anyone familiar with the system will likely be able to guess as functionally they remain largely the same, so there's no need to hide it either. 

The key difference is context. Most things have been altered to fit in a science fiction setting, with one of the key differences being that the element of magic has been changed into an element of technology, including the source of power and the type. In the same way that something might be more or less magical in traditional D&D, the Atlas equivalent will be more or less technologically advanced, with hi-tech referring to advanced things like holographic displays and traversable energy fields, and analogue referring to low tech solutions like manual control panels and bulkhead doors. These things are supposed to blend together seamlessly in the world, and in the same way that a ranger might use a bow and dabble in some spells, the Atlas alternative- a pilot, could use a pistol, and have a reserve of high-tech gadgets. Functionally the same but more appropriate for an interstellar voyage to alien planets.

Building on this, something new (but not really) that this supplement brings to the table is a comprehensive system for building and operating vehicles and spacecraft. This is something that at face value might seem complicated, but in actual fact is once again a conversion of familiar mechanics. In short, vehicles and spacecraft are additional characters that the players can utilize for their adventures, but on a shared basis as opposed to belonging to an individual. They have their own stats, progress in the same way that agents do, and have their own inventories, classes, backgrounds and so on, they are just controlled by agents and NPCs in game.

There are a few more minor changes, tweaks and modifications to the game as a whole, but by now hopefully you have a decent understanding of what Atlas Moment is aiming for. The system was designed as an answer to the multitude of different science fiction systems available out there to play, that gives game masters a chance to combine all of their favourite parts of the worlds they know and love into one comprehensive system, without being tied to any particular property. A love-letter to the genre that lets everyone live out their cosmic dreams.