Just another time nerds, to break down Window functions to you in the simplest form ever.
Simply window functions allow you to perform calculations across a set of rows(a window) while still retaining access to individual rows.
You can use these functions to perform running calculations.
They include:
RANK(), ROW_NUMBER(), DENSE_RANK(), LEAD(), LAG() and even other more aggregate functions.

For the ranking functions:
Row_number(): numbers all rows sequentially
Rank(): uses the same numeric values for rows which are a tie
then skips the next value
Dense_ rank(): uses the same numeric values for rows which are a
but does not allow any gap to the values.

Lead () allows access to rows after the current row while lag() allows access to rows before the current row.

Syntax:
RANK() OVER(PARTITION BY... ORDER BY... )

Partition by divides the result set into partitions
The ranking gets applied to each partition separately

This will help you get started with window functions
Anything and Everything Data