what do i to open and edit a picture that is saved to iPhoto?
Assuming you have Photoshop and Bridge (because you are in an Adobe forum, not Apple iPhoto) there has probably gone something wrong with your install. After you have installed Photoshop in a proper way the files should automatically open in PS. But in your case go to Finder, select the file type you want to open in PS for editing and use the 'get info' command.
Somewhere halfway you should see the option for 'Open With'. Choose your installed version of photoshop and also include 'change all' to apply on all files of this type. Repeat this for other file types (jpeg, tiff, PSD etc) you want to open in PS.