"Those men are young and handsome."
Translation:Ti muži jsou mladí a hezcí.
Nope, "hezký" is for masculine singular, in this case "muži" is masculine animale plural and so it is "hezcí". The grid will clarify all your doubts :) https://en.wiktionary.org/wiki/hezk%C3%BD#Declension
I will try to explain the difference by example, but one of the one of the Czech natives on the team may do a better job. :-)
In the first case example, we are saying that some particular men that we see are young. Our sentence describes a characteristic of each individual man.
"Those men are young" = Ti muži jsou mladi.
In the second example, we are saying that a group of people that we see consists of young men. Our sentence -- in a way -- describes the group.
"Those are young men" = TO JSOU mladí muži.