Google Photos now details the people it recognizes in pictures simply by tapping on the info icon when browsing a picture from your Google Photos library. The info icon is nothing new of course, but since one of the last couple of versions Google Photos was updated to include a new section on the info page for pictures that have people in them when it has recognized those people. This doesn't appear to show up unless there is recognition, so you may end up seeing pictures on your library with people in the photos but with no additional "people" information about that person.
When Photos does recognize someone there will be a "people" section that is listed just above the section that's labeled "details" where you can find all of the technical information about your photo, like the aperture type, ISO, the phone used, and the photo's location. In the people section there isn't a lot of information, in fact the only thing listed here is the names of the people that have been recognized along with a small thumbnail of them, and that's it. This might not seem like much but it's an extra bit of info you may not have otherwise had and it serves as a sort of automatic tagging of the person in the picture.
With Google Photos now listing these details, the only thing missing in regards to tagging people in pictures is the actual ability for people to tag someone. The app is still missing this particular element, but Google has at least now made it so that tag details will be there when the app is able to tell who the person is. If you don't see this feature in any of your pictures inside of the Google Photos app it's possible that you may not be on the version where it was implemented, or Google Photos may have just not recognized the people in your pictures. This small change is just one of the latest additions to Google Photos that Google has included recently, though there are more interesting features to look forward to like the archiving feature that was discovered last month.