I updated my mac and I can't use Iphoto.

iPhoto, being a 32 bit application, is not compatible with the Catalina macOS.

iPhoto was replaced with Photos which should be in the Dock. It will definitely be in the Applications folder. To migrate your iPhoto library either drag and drop your iPhoto library onto the Photos app or launch the Photos app with the Option key held down and in the Open Library window select your iPhoto library to open.

Correct. iPhoto was discontinued 5 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.

:)