"The boy and the man are happy."
Translation:Taoba valā kirini issi.
How do you know if you must put "issi" (or iksi...) behind an adjective?
Well, issi/iksi is the verb of the sentence, and High Valyrian is a language where the verb is put at the end of a sentence. As for which one to choose: "issi" means "they are" and "iksi" means "we are".