Hi,

You can do it in several ways :)
If you need to select a group that has visited a URL, please select the Ad hoc rule.
You can find it in Segmentation -> Ad hoc.
In place of URL domain -> choose your domain.
Then, in place of the URL pattern, select a phrase from the URL that points to the category you need. Let's assume you want to tag people who visited the skincare category. Then the URL phrase will simply be SKINCARE - as in the example below.
https://www.cosmetics.com/collections/skincare
In Tag, enter your tag with which you want to tag people who visited the URL.
After triggering the rule, your tag will be ready in a few minutes :)

Remember that the ad hoc rule is used to tag contacts who visited the URL in the last 30 days.

If you want to tag contacts all the time, you can set up a simple automation rule.
Just select from events ->
The contact visited the url, then select the domain and phrase from the url (as in ad hoc), then add the element from the action -> Add tag to the contact.
Thanks to such a rule, tags will be assigned on an ongoing basis.