What is the group by keyword and what does it do in SQL code example

Example 1: group functions in sql

Multiple Row Functions (Group functions, Aggregate functions):
(Count, MIN , MAX, AVG, SUM)
will run for multiple rows and return a single value

Example 2: what is group function in sql

--- GROUP FUNCTION | MULTI ROW FUNCTION | AGGREGATE FUNCTION 
--- COUNT , MAX , MIN , SUM , AVG