iPhoto can no longer run on macOS 10.15 Catalina. iPhoto needs some old, outdated system frameworks, that are no longer provided by Catalina.
Apple released the Photos.app as a successor to iPhoto. You can open the iPhoto Libraries in Photos.
Launch Photos (you will find it in the Applications folder. The icon is showing a flower with rainbow coloured petals). Hold down the options key ⌥ while laughing Photos until the dialog to select a library appears. Select your iPhoto Library. Photos will create a new Photos Library from the iPhoto Library. You should find all photos and albums in the library. The iPhoto Events will appear as albums as well.
As an introduction to Photos see the user guide: Photos User Guide for Mac – Apple Support (UK)