To view the filter, click "Show Filter" on the report page.
You can see the filter that suggest properties and values to filter by.
If you see the message "We do not register any tags to filter by." instead, make sure you have enabled collection of Usetiful tags in your privacy settings. If you changed your settings to start collecting tags, it may take some time until will be loaded first tags.
Field accept conditions in format tagName operator value and you can specify as many conditions as you want. Between each condition there is AND logical conjunction.