One of the most complicated thing to explain to a non-spanish speeker is the difference between "Ser" and "Estar" verbs, because both has different meanings and usages, by other hand, both are translated as the same in english, in this case "To Be". But in simple words, "Estar" is more related to temporary location or a certain state or mood. Estoy feliz: I'm happy (now) - I'm in a state of happiness. Estoy en casa: I'm at home - I'm located at home in this moment. "Ser" is more related to adjectives and is the most direct verbs for describing people, things or whatever, off course whatever that you are describing has the meaning of a permanent statement. Soy feliz: I'm happy - I define or decribe myself as a happy person. Soy alto: I'm tall.

if you use "Soy" you are talking about who you are as people, your being, your identification . it means that you are a happy person. If you use "Estoy" you are talking about the way you are feeling in an specific moment, a temporary condition.

Estoy feliz, se refiere a ese momento en particular; Soy feliz, se refiere a un contentamiento continuo o general

Estoy feliz en este momento / Soy feliz en general.

Estoy feliz: I'm happy (now, today, at the moment) Soy feliz : I'm a happy person; I'm happy (with my life; with my current situation in existence)