A naive question about safties

I have been watching football a long time, but could someone tell me what the difference between strong safety and free safety is? I think I know what they do differently, but how does someone decide when looking at an athlete which position would fit them better? What is the skill difference? If you were drafting an athlete, what skills would categorize them as a strong safety, a weak safety, or a cornerback?

Thanks for educating a long-time fan.

 

normally ss play the run and is more like another lb but deeper , fs play center field and help in pass coverage is more like another cb in the middle .
in cover two the two safeties are both fs and split the deep middle of the field
that's what i undestand (not sure is right )

 

The strong safety is responsible for the tight end most of the time and is called on for run support. The free safety has varied assignment based on where the corners go and the receivers in the pattern.

I played safety in college but in most of our defenses both safeties were primarily run support. There were very few four receiver packages.