Located on the Recent Attendance tab this Condition allows you to enter a value (the percentage) with a comparison (Equal, Greater Than, etc.). You can also specify a Program or Program/Division or even Program/Division/Organization. The results will be those matching the attendance percentage.
For Inreach purposes, you want to find those who have a low attendance percentage in Adult 1 Life Groups so that you can contact them. Use LessEqual and then whatever percentage you want - probably something like 20.
If you are interested in attendance percentages within an organization, we have a better report for that.