GROUP BY and ORDER BY commands

While writing a query for an aggregate function, it becomes difficult for me to determine which column is right to go with GROUP BY command or ORDER BY command. Please help!
https://www.codecademy.com/paths/data-science/tracks/analyze-data-sql-analyze-real-data/modules/analyze-data-sql-usage-funnels/lessons/sql-funnels/exercises/compare-funnels