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Before writing any M code, understand what kind of language you're working with. M is functional, immutable, and lazy. These three properties explain most of its surprising behaviors.

The let/in block is M's fundamental building block. Every query you write is a let expression. Learn how named steps compose into a pipeline.

M is strongly typed. Learn the primitive types, how nullable types work, and why type annotations on Table.AddColumn columns matter for performance.

Null propagates silently through M expressions. Learn how null flows through comparisons, arithmetic, and function calls — and how to defend against it with the ?? operator.

each is shorthand for a single-argument function. It appears everywhere — in Table.AddColumn, List.Select, List.Transform, and more. Understanding it unlocks the whole standard library.

M functions are first-class values. Learn how to define reusable functions, pass them as arguments, and compose them to eliminate repetition in your queries.

Errors in M are values, not exceptions. Learn try/otherwise, how to catch errors cell-by-cell in a table, and when to let errors propagate versus recover from them.

Query folding is M's most important performance concept. Understand when M pushes work back to the data source, when it can't, and how to keep your queries fold-able.