At times you may want to view only a portion of your contact list rather than viewing all contacts at once. There are many segmentation options at your disposal.
You can view only contacts who belong to certain default or custom segments, for example contacts who:
opened or clicked an email or part of other email campaign metric
belong to a subscription list
match custom segmentation criteria: you need to use filters for this
...and many more
Click on the number that appears next to a metric or label on various list and reporting pages to view the contacts that belong to that metric..