Firstly, how to transfer photos from iPhone to Mac.
Connect the device to your Mac. Here are three ways:
1. Drag files or folders from the Finder to the Photos window.
2. Drag files or folders from the Finder to the Photos icon in the Dock.
3. In Photos, choose File > Import. Select the photos or videos you want and click Review for Import. If you selected multiple photos or videos, select the ones you want to import and click Import [number] Selected or Import All New Photos.
Secondly, how to transfer photos from Mac to iPhone 4s.
Connect iPhone 4s to your Mac, and open iTunes.
Choose your iPhone, click "Photo", select a folder, and then choose "Sync".
Important Note: When syncing photos from computer to iPhone or iPad with iTunes, you will lose all the previous photos stored in Photo Library.
Hope this can help you.