"He is kind."
Translation:Ille est benignus.
Benignus is in the nominative and benignum in the accusative case. The verb to be (est) always goes with the nominative case. So: "Ille est benignus." (He is kind. - nominative), and to take another example from Duo: "Patrem benignum habeo." (I have a kind father. - accusative).
Copy-pasted from https://www.textkit.com/greek-latin-forum/viewtopic.php?t=10061:
ille is a demonstrative and can generally be translated as "that". So, ille vir is "that man", illa femina is "that woman" etc.
Is is a personal pronoun. It generally means "He". So you could have is est avarus, "he is greedy". Confusingly though, Is, along with Ea and Id (the fem and neuter parts respectively), can also act as demonstratives. So you could see Is vir which basically is the same as ille vir, "that man". A good rule of thumb is to translate "Is" as a demonstrative (that) when it comes immediately prior to a noun, and as a pronoun (He) the rest of the time.