Read this chapter if you are familiar with roleplaying games in particular, but not with Blades in the Dark or other games based on it. This chapter will focus on how this game differs from other roleplaying games you might know.
As you will notice in the chapter on Action Rolls, resolving something in the game is more complex than in most other games, with a whole setup process before you even roll the dice.
However, in total the game is much less complex as actions are much larger and contain much more. A roll is not equivalent to one attack, but can be an entire combat sequence with multiple attacks, defences, dodges, tricks, etc.
The same is true for non-combat actions, with each roll resolving an issue to its conclusion.
Also note that there are no rolls for defence, resistance, no saving throws or armour rolls. Everything is figured into that one action roll.
So while more effort is put into individual rolls, you roll a lot less often.
When playing Fallen Empire you will quickly notice that the GM almost never rolls dice. This frees the GM up to focus more on the story, the villains and the action.
Instead, NPC actions are either resolved together with player actions, such as in combat where your player roll also determines if you were hit by the enemy, or the GM simply announces them as happening and players can choose to resist them (at a cost).
Unintuitively, this gives you as a player more agency. In most games, if the party runs into an ambush, the GM will roll a couple of dice and announce who was hit by the arrows suddenly flying out of nowhere. In Fallen Empire, the GM will simply announce that everyone gets hit by a few arrows and takes a certain amount of damage, and then the choice is on the players to bring their shields, armour or Resistance Rolls out to resist this damage, avoid being hit altogether, or to take the hit and save those resources for another time.
What might take some getting used to is that you choose these things, instead of having them as results of the dice.
Instead of long preparation, Fallen Empire (like all Forged in the Dark games) goes straight to the action and lets you flash back to preparations you are assumed to have made. The main mechanics for this are the explicit Stress > Flashback and the fact that you can choose equipment during the adventure.
Both of these take some getting used to, but are powerful game mechanics that speed up the game and make it flow better.
A unique feature of Fallen Empire is that you can start playing almost instantly, as your character is created during the game.
Similar to other games, you create your character with a number of character points. Unlike other games, you don't have to spend all or even any of them at the beginning, but can do so during gameplay.
So in most cases, where you have a rough idea of what kind of character you want to play, you will just quickly assign maybe half your points to the things your character will obviously need and then put down the remaining points during play when you reach those "actually, I think my character would be able to do that" moments.
Unlike most games, the time between adventures is structured in Forged in the Dark games, which has two effects.
First, it allows players to get things done and use the time, in a structured way. Downtime Activities are an important part of the gameplay and also allow for a more stress-free environment for character development and roleplaying.
Second, characters may well start adventures not fully rested. That is an unusual idea for most players of more traditional games, as well as for GMs. It means that they could still be injured, low on mana, etc. when a new adventure begins. They may not have had enough downtime activities, or preferred to spend them on other things.
This follows the principle of player choice and consequences. You can run errands while badly wounded - but if you don't get the rest the healers advised then, well, you don't heal up.
It also means that getting through an adventure without wounds is rewarded over crawling over the finished line with all your resources spent. It makes consequences within the adventure more meaningful and last beyond the immediate adventure.
Forged in the Dark systems like Fallen Empire offer you as the player much more agency than other roleplaying games. Keep in mind that very few things in the game are not subject to some negotiation or trick you can pull out of your sleeve.
If you are unhappy with the odds of an action roll, for example, you can at any point before actually rolling the dice reconsider and try something different. Maybe another approach will give you better odds. Or you can ask for assistance from other characters, or invest Stress yourself to gain a bonus die and/or higher effect. If the roll is important, you can spend Tension and ask the GM if there is a lucky break in the cards for you.
The same is true when you are not acting. Almost anything that happens to your character can be resisted (at the cost of stress). This includes not just damage, but all other kinds of Consequences.
And if the situation seems utterly hopeless, you can still run a flashback to retro-actively set up more fortunate circumstances.
Most of these options come at a price, most often stress, so the game is less about what inevitable happens to your character and more a game of what you, the player, let happen, be it for the sake of the story or because you want to conserve resources for more important encounters.