You can filter reports by product tag, customer tag and order tag.
Let's walk through an example with product tags. The method is the same for customer tags and order tags.
a) Click on Add filter
b) Click the field named Product is tagged with
c) A dialog appear where you can search for the desired tag
d) Press OK. A filter is added that matches only rows for which the product is tagged with the chosen tag.
To switch to another tag, remove this filter and repeat the steps above.
Note that you can add multiple tag filters. For example, you might want to filter products that are tagged with both Pants and Summer. Or, you could filter products that are tagged Pants but NOT tagged summer.