A sunroom is more of a 4-seasons room that's usable year-round; Think of a room with large windows that are closed for an extra insulated room for the winter months, but open during the spring and summer for the outdoorsy feel. A screened porch is exactly that: a screened-in porch.
You may see similar features such as ceiling fans and/or infrared heaters in sunrooms and screen rooms alike, however only the former is viable for use (in our area, with our extreme seasons) 4 seasons out of the year.
Houzz is another great resource for answering those sort of questions, as well as finding ideas and professionals (with reviews) all in one place. If you're interested:
https://www.houzz.com/ideabooks