Apple stopped the development of iPhoto in 2015 and pulled it from the AppStore. There have not been any updates since. And when Apple dropped the support for 32-bit software with the release of macOS 10.5 Catalina, it has been the last nail in the iPhoto coffin.
Photos is the successor to iPhoto, but is very different and may be confusing, if you expect it to be working like iPhoto. It is quite powerful, but the primary design goal of Photos for Mac is to give a unified experience for the users when using Photos across all kinds of Apple devices, from the Mac to the iPhone, with all devices perfectly in sync by using iCloud photos as the central storage. And Photos has been designed to free us from the trouble of having to create the basic structure of our Photos Library ourselves. Photos is coming with many predefined views, ready to use. We can automatically browse the photos grouped by the day, month, years they have been taken, by the location they have been taken, by the people in them, by the media kind. Photos is trying to understand the contents of the photos, and classifies them according to the categories of the objects in them or the kind of scene. For example, when I search for the category "Birthday", Photos will show all photos taken on my birthday or the birthday of a close family member. We only have to create albums or keywords for categories, that Photos cannot create automatically. Because Photos is so different, it may help to have a look at the user guide, before you try to explore it.
See also: Updating from iPhoto to Photos for macOS (archive copy)
And the Photos User Guide to get started: Photos 5.0 User Guide for Mac - Apple Support
Also: Photos Support website
