Inlay hints appear in the editor and provide you with additional information about your code to make it easier to read.
Parameter hints appear next to a parameter in a function call show you the name of the parameter from the function definition.
Return type hints are by default shown for chained methods that are split between multiple lines and return at least 2 different types. The type information is inferred from a JSDoc comment or based on the static analysis of your code.
Type hints show a variable type or a function return type next to their definition. Type hints look very much like type annotations in TypeScript.
In inlay hints settings you can configure which types of information you want to get in hints.