Translation:I am happy.
기쁘다 means "to be glad". How do you differentiate between happy and glad in English? Of course they're similar but I don't use them the same way all the time. Happy seems to me to be a constant state of being but glad seems to be an instance, as in "I'm glad you had a good time" vs "I'm feeling pretty happy these days".
행복하다 means 'to be happy' and 기쁘다 means 'to be glad'. Usually, the first has a stronger meaning than the second.
기쁘다 is an inherent adjective, but 행복 is a noun, made into an adjective as 행복해 or 행복합니다 which is like "being happy"
Everyone else makes a good point in terms of translation, but what about usage? How does 항복하다 differ from 기쁘다 in terms of how/when they might be used in conversation?