QUICK ANSWER
"Se ha" is a form of "se ha", a phrase which is often translated as "it's". "Sé" is a form of "sé", a phrase which is often translated as "I know". Learn more about the difference between "se ha" and "sé" below.
se ha(
seh
ah
)A phrase is a group of words commonly used together (e.g., once upon a time).
a. it's
El verano ha sido estupendo, pero se ha pasado rapidísimo.This summer has been great, but it's passed by really fast.
b. it has
El cerrojo se ha atascado. No sé cómo vamos a abrir la puerta.The bolt has got stuck. I don't know how we're going to open the door.
c. she's (feminine)
¿Sabes algo de Rosa? - Sí, se ha divorciado y se ha ido a vivir a Madrid.Have you heard from Rosa? - Yes, she's got divorced and has gone to live in Madrid.
d. she has (feminine)
Mi hermana se ha comprado una casa muy cerca de la mía.My sister has bought a house very close to mine.
e. he's (masculine)
No sé a qué hora llegó anoche, pero se ha pasado el día durmiendo.I don't know what time he arrived last night, but he's been sleeping all day.
f. he has (masculine)
El actor se ha retirado del cine para dedicarse a la política.The actor has retired from movies to go into politics.
i. no direct translation
This refers to an idiomatic word or phrase for which there is no word-for-word translation.
A Candela le ha tocado la lotería y se ha despedido del trabajo.Candela won the lottery and left her job.
Esta mañana se ha quedado dormido y casi no llega a clase.This morning he overslept, and he almost missed his class.
sé(
seh
)A phrase is a group of words commonly used together (e.g., once upon a time).
a. I know
Sé que eres tímido y que no te gusta hablar en público.I know that you're shy and you don't like speaking in public.
b. I know how
Sé tocar el violín, pero no soy un músico profesional.I know how to play the violin, but I'm not a professional musician.
3. (informal) (imperative; second person singular; have existence)
A word or phrase used to refer to the second person informal “tú” by their conjugation or implied context (e.g., How are you?).
