how to transfer photos from Samsung S4 to my Mac

You need to connect your phone to your Mac with a USB cable and (if it doesn't automatically) open your photos app, select the phone in the sidebar, select the photos and import them.

You upgrade iCloud with Apple, I'm not sure what the other part of your question relates to.

If your Samsung follows international standards for cameras then it will work fine - if it does not then you need special software from Samsung or a third party - Apple supports all standard devices - non-standard devices need additional software from another source

A web search or asking Samsung support is the way to find Samsung information

LN