Current

The TypeScript team, and other TypeScript involved teams, created a TSDoc specification. https://tsdoc.org/

Example straight from the docs:

export class Statistics {
  /**
   * Returns the average of two numbers.
   *
   * @remarks
   * This method is part of the {@link core-library#Statistics | Statistics subsystem}.
   *
   * @param x - The first input number
   * @param y - The second input number
   * @returns The arithmetic mean of `x` and `y`
   *
   * @beta
   */
  public static getAverage(x: number, y: number): number {
    return (x + y) / 2.0;
  }
}

Past

TypeScript uses JSDoc. e.g.

/** This is a description of the foo function. */
function foo() {
}

To learn jsdoc : https://jsdoc.app/

But you don’t need to use the type annotation extensions in JSDoc.

You can (and should) still use other jsdoc block tags like @returns etc.

Just an example. Focus on the types (not the content).

JSDoc version (notice types in docs):

/**
 * Returns the sum of a and b
 * @param {number} a
 * @param {number} b
 * @returns {number}
 */
function sum(a, b) {
    return a + b;
}

TypeScript version (notice the re-location of types):

/**
 * Takes two numbers and returns their sum
 * @param a first input to sum
 * @param b second input to sum
 * @returns sum of a and b
 */
function sum(a: number, b: number): number {
    return a + b;
}