To see all contacts currently within an Audience, start by navigating to the Audiences menu, then click on the name of the audience you want to look into.
On the following page you will see a full list of individual contacts currently* within the audience.
You will also see the rules that govern this audience, e.g: these contacts all have the tag of Upsizer, and have a buying requirement of a minimum of 4 bedrooms.
* As contacts match, or no longer match these rules (for example in this case, as tags are added or removed; or contacts update their buying preferences), they will be automatically added to or removed from the audience.
You can edit the existing audience by modifying its filters.