How do I set a filter on a mission?

To set a filter on the mission, go to the fourth tab at the bottom of the page when creating a mission under 'Audience'. Once here, click the tab 'Advanced Audience Settings'. Here you can set the filter of the mission by clicking filters such as gender, reach and many more. Once the filter has been selected, check it is correct and then select 'Add user to audience'.  You will notice that the number under 'Selected Audience' will change in accordance. Once done, move on to the publish page and the filter will be saved.