Difference between scalar, table-valued, and aggregate functions in SQL server?

Question

What is the difference between scalar-valued, table-valued, and aggregate functions in SQL server? And does calling them from a query need a different method, or do we call

Answer 1

A scalar function returns a single value. It might not even be related to tables in your database.

A tabled-valued function returns your specified columns for rows in your table meeting your selection criteria.

An aggregate-valued function returns a calculation across the rows of a table -- for example summing values.