How do I create a filter in Gmail?

1. Open Gmail.
2. In the search box at the top, click the Down arrow
3. Enter your search criteria. If you want to check that your search worked correctly, see what emails show up by clicking Search
4. At the bottom of the search window, click Create filter with this search. 
5. Choose what you’d like the filter to do.
6. Click Create filter.

Note: When you create a filter to forward messages, only new messages will be affected. ​Additionally, when someone replies to a message you've filtered, the reply will only be filtered if it meets the same search criteria.