There are lots of guides you can find talking about "Alignment" in D&D (including Wikipedia). The focus of our game is on story rather than categorization, however, so this allows nuance and point of view: we will always try to consider the motivations and shortcomings of the characters (including NPCs). The big deal characters that matter will not be simplified into acting because of their category.
However - the alignments are also a foundation of how the D&D multiverse thinks about the forces and conflicts, so it helps to understand a little about some of the differences at least "in the corners". For example - the difference between the Nieznane (devils and demons) (and the "Blood War" between them).
Lawful vs. Chaotic
This is probably the easier to understand. It comes down to preference for Order and Rules (and consistent routine vs. variety). Those with a "Lawful " alignment believe:
- There should be laws (or at least rules)
- There should be enforcement of these rules
- The rules should be followed and respected
The opposite alignment is "Chaotic " - which does not necessarily mean being against this list. One might break rules if they lack the ability to understand or comply with the rules, if they outright desire to destroy all order, they believe rules to confine their nature as a "free spirit", or just for fun.
Of course there is a lot of room for rules to go from building an orderly civilization ("no murder or theft") to being imposed to dominate others ("execute traitors" or "serve the Emperor") - but that comes down to the other part of alignment: Good vs. Evil.
Good vs. Evil
These mostly have to do with empathy for others . How do my actions impact those beside myself? This gets grey mostly in terms of who is included in the "others". A unicorn, perhaps one of the most iconic symbols of good, may have little to no empathy for whole races (like Orcs). But in general, player characters (PCs) will lean to good in that it aligns with the stories of heroes and acting your part in a story not because you are selfish or power-hungry, but because you care about doing "what is right" and helping others.
This comes down to genuine interest in understanding other individuals, groups, and their struggles and thinking how your actions will make things better or worse for them.
Simplifying the world as colored black and white for evil and good can also be a big mistake. The stories we have already told include several important alliances between the parties and evil characters. Sometimes this has to do with having a common enemy or purpose (like cooperating with Vellynne Harpell or Claugiyliamatar / "O.G."). While it is natural for good to join forces (a benefit of caring about others), evil can be its own worst enemy (two self-centered power-seeking rivals - or most dramatically, the Blood War between devils and demons).
Neutral
The term used when a PC or NPC is indifferent to Law/Chaos or Good/Evil is "Neutral". This can come from being extremely focused on or embodying the nature of one of the four above, such as:
- Lawful Neutral: The law and rules are paramount and override all other considerations.
- Neutral Good: Caring for the wellbeing of others regardless of the rules or taking action to change or break them.
There is also a concept of "True Neutral" - believing in the importance of balance between the extremes (or in simple lifeforms like beasts, lacking the mind to do more than simply be whatever creature you are - eat, grow, raise young, etc.)
Examples
- Lawful Good: Captain America, Superman, Katniss Everdeen (Hunger Games), Obi-Wan Kenobi
- Lawful Neutral: Nick Fury, Odin, Stormtroopers, Machines/Computer Programs
- Lawful Evil: Dr. Doom, Ronan, Ultron, Darth Vader, Sauron, Scar (Lion King)
- Neutral Good: Peter Parker, Captain Marvel, Harry Potter, Luke Skywalker
- True Neutral: The Watcher, Gamora, Treebeard, Severus Snape
- Neutral Evil: Voldemort, Smaug, Deathstroke, Scarecrow, Jason (Friday 13th)
- Chaotic Good: Robin Hood, Star Lord, Iron Man, Han Solo, Sirius Black, Fred Weasley
- Chaotic Neutral: Jack Sparrow, Loki, Deadpool, Hulk (out of control), Catwoman
- Chaotic Evil: The Joker, Hela, Demogorgon (incl. Stranger Things), Bellatrix Lestrange