I do not know how to retrieve my photos? They were in the iphotos app

iPhoto has stored your photos in an iPhoto Library, not in the iPhoto application. By default you will finf your iPhoto Library in the Pictures folder. Look there for your iPhoto Library. Photos can create a new Photos Library from it, this library will be created in the same folder as the original iPhoto Library.

iPhoto was discontinued 6 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.