1. The verb gustar means "to be pleasing" and it always has an indirect object pronoun with it to say TO WHOM it is pleasing. Do NOT learn it as the verb "to like" because that will get you into trouble! The sentence should be:
A su novio no le gusta los niños. = (TO her sweetheart the kids are not pleasing. OR freely translate as "Her sweetheart does not like the kids."
Feel free to ask for more explanation if this doesn't clear it up for y ou.
2. The difference between ser (to be) and estar (to "seem"/to be). It is either "es bueno" or "está bien" = Este profesor nos dijo a nosotros que el ejercicio no está bien. = This teacher told us (you need the indirect object pronoun in front of the verb and what is dispensible is "a nosotros" after the verb to say TO WHOM he said th is. "no es bueno" = it isn't good OR "no está bien" = is not OK (freely translated)
3. Without the English, I'm not sure what you saw and that is important to know if you should have the Present Indicative (for fact) = pones OR Present Subjunctive (that you may put = in the future). Based on what I see, it must be: "Tu éxito depende del esfuerzo que pones." = Your success depends ON (depender takes DE and not EN) the effort you put.
4. esperar means to wait FOR. The "for" is hiding inside the verb so you add neither por nor para. The sentence has to be: "He esperado a mi hermana durante horas." = I have waited for my sister for hours. It DOES require a "personal a" because my sister is a direct object and she is a person. Ask about "personal a" if you don't understand that point.
5. entrar EN and salir DE = just memorize those because you enter INTO somewhere and exit FROM somewhere. The sentence should be: "No puedo entrar en la casa." = I can't/I am unable to enter (into) the house.
1.- A su novio no le gusta los niños, It is wrong, has to be:
A SU NOVIO NO LE GUSTAN LOS NIÑOS.
2.- Este profesor nos dijo a nosotros que el ejercicio no está bien, It´s redundant
It is better
ESTE PROFESOR NOS DIJO QUE EL EJERCICIO NO ESTÁ BIEN.