How to use full join ?

Answer 1

please be more specific. and why don't you google it? the first thing that comes is pretty useful.
https://www.w3schools.com/sql/sql_join_full.asp

Answer 2

The FULL OUTER JOIN keyword returns all rows from the left table (table1) and from the right table (table2). The FULL OUTER JOIN keyword combines the result of both LEFT and RIGHT joins.