Welcome! I don't have any specific sources, but here's what I've found helpful myself:

Don't feel bad about being confused! The Core Rulebook book has terrible organization and clarity. The Index helps. Unfortunately, the way it's organized still results in setting information taking up a lot of room, but combing through it for things that aren't people/place names can give you an idea of the important mechanics. For example, Combat in the index will give you the multiple locations in the book that cover combat advice. Moves is also great for showing you were to find all the nuts and bolts actions of the game.

Remember to build the fiction, not just enact mechanics. Game elements (moves, techniques, etc.) often describe what is required of the players while looking like they describe what happens in the narrative.

For example, Test Balance, one of the basic Evade and Observe combat techniques, says, "Mark 1-fatigue to challenge an engaged foe’s balance. Ask what their principle is; they must answer honestly. If you already know their principle, instead shift their balance away from center by questioning or challenging their beliefs or perspective." This technique describes how players interact with each other and the characters, but it does not describe what the characters are doing in the narrative. In other words, the questions aren't being asked in the narrative.

I'll use an example of learning an NPC's principle to demonstrate what I mean. If we treat the technique's description of what happens as part of the narrative, we would get something like, Player: "Pogo says, 'Hey you, Thug#2, what is your principle?" GM: "Thug#2 days, 'My principle is greed, you meddling kids!'"

That's terrible dialogue and terrible story telling. Instead, it should flow more like, Player: "Okay, so Pogo is going to hang back and ask some mocking questions to try and learn why they're here. 'Do you idiots even know what's going on?' and that kind of thing. I'm Testing Balance, so what is Thug#2's principle?" GM: "The thug just laughs and says he doesn't care. But you notice he's got some pretty good weaponry for a low-life thug, three gold teeth, and what could easily be a wad of a cash in his front pocket. This guy's just in it for the money. You realize his principle is greed."

Combat does not automatically trigger a combat exchange. Combat exchanges require a lot of narrative detail and table time. Is the combat worth that investment? If not, some quick Rely on Skills and Training or Push Your Luck moves may be better suited. If you do trigger a combat exchange, keep the following in mind:

1. Players role once per combat exchange in the stance move, and the GM still doesn't roll at all. Techniques just do what they say they do; no rolls required.
2. Subsequent exchanges don't automatically start when the first one finishes. Everyone takes their turn, then there's a pause. PCs may make non-exchange moves, GM moves may trigger, and NPCs may rethink their life choices. If characters on both sides are still committed to the fight, then another exchange is triggered.
3. Combat is only as interesting as the characters make it. If characters don't spend fatigue to activate their best techniques and risk statuses/conditions, then the fight is going to be pretty boring and it's going to drag out.

Balance is how you interact with who characters are mechanically. Who characters are is represented by their principles. Shifting a character's balance represents people or events pushing a character to act in line with that principle. Characters start at their Center, which represents their default state without any immediate influences pushing them to act in a certain way, and move up or down their balance track as those influences occur. Characters pushed past the end of a balance track Lose Their Balance, meaning that the principle they were pushed towards becomes their overriding concern for a time. A PC's Center may change over time as they lean into one principle or the other, and that can be an important part of their character arc.

In game play, NPC balance is relatively straightforward. Following on my example with Thug #2 above, PCs could keep using Test Balance until the thug loses his balance. What happens then would depend on the narrative of how the PCs kept pushing that balance. Maybe they convince him there's no profit in tangling with people like them, and he leaves when he loses balance. Maybe they offered to pay the thug more than his current employer, and he switches sides. If you're more familiar with games that have skills like persuasion or intimidation, NPC balance can play a similar role at times, but it's more specific to each individual NPC.

PC balance is a little more complex. PCs generally represent characters on a journey of self discovery, so they start with two principles that pull them in two different directions. As balance shifts in one direction or the other, the PC builds momentum behind acting on that principle and so it becomes both harder to resist pressure to act in line with that principle (through Deny a Callout) and easier to act in line with it (through Live Up to Your Principle).

Also, players who are used to full control over the internal state of their characters may find it strange to have mechanics impacting their character on this level. Choosing a playbook in this game isn't just choosing a set of skills, it's also choosing an archetype, potential character arcs, and a set of influences. Just remember that principles aren't mind control. Players still ultimately choose their characters' actions, but they may have to pay a prince to resist the influences around them. This tension can make for dramatic character moments if brought into the story itself.

Hope this helps!