I view allignments for players more in the same vein as bonds traits ideals and flaws, it helps provide a shorthand summary to inform the basic nature and predisposition of actions of a character, As i understand them the various allignments could probably be summarised as such:
LAWFUL: consistently obeys and follows a strict code or set of rules, even when going against them would be beneficial to the individual, the rules in question may be the local law, divine or infernal commandments or just a personal code, so long as they are consistent and are followed, however a lawful entity may use the laws in service of their own intentions or apply them in circumstances against the spirit of the law.
L/C-NEUTRAL: typically obeys rules and orders unless given a reason or it would be in their benefit not to, but are not overly inclined to enforce them either unless, again, it is to their their benefit to/detriment not to.
CHAOTIC: has no consistent code of conduct and generally does as they wish in any given moment irregardless of any laws, customs or expectations that might otherwise hinder them, this does not mean they will not exploit any existing laws or suchlike if it is to their benefit to do so.
GOOD: tries to improve, protect, respect and benefit the lives and circumstances of others, generally without expectation or motivation of rewards for doing so, sometimes but not inherently, even at a detriment to their own lives or circumstance.
G/E-NEUTRAL: cares about and considers their own lives and circumstances before considering other people's, however they will not seek to needlessly inflict suffering or try to benefit themselves at the cost of others, they may also go out of their way to assist or benefit others if it is in turn to their own benefit or at least not significantly to their own detriment to do so.
EVIL: seeks to improve the lives and circumstances of themselves (and generally their own close company) without caring about the effect on others in order to do so or seeks to harm the lives and circumstances of others, may go out of their way to needlessly inflict suffering and strife for no inherent reason, does not respect or care about the lives or circumstances or rights of others.
The measure of 'what is good and evil, lawful or chaotic' is laid out by the game rules and thus in and out of universe that is how those terms are defined for the purpose and the context of DnD, and they are broad and all-encompasing enough that even if you choose not to or outright refuse to actively assign any allignment to your character that doesn't mean they don't allign with one anyway, either that or you're playing them inconsistently.
(As it is now, and i understand it has been different in the past or at least has been used to do so) Your allignment isn't something that controls your character, it is something that is defined by them and their actions.