Refiere a una situación hipotética y se forma según la estructura if + simple past + simple condicional. Aquí tienes algunos ejemplos traducidos.
If clause
If +Past Simple
If I won the lottery,
Main clause
would / could / might + verb
I would travel around the world.
If I won the lottery, I would travel around the world.
Si ganara la lotería, viajaría por todo el mundo.
If I were in Brazil, I would go to Rio de Janeiro.
Si yo estuviese en Brasil, iría a Río de Janeiro.
If I were you, I would buy that car.
Si yo fuese tú, compraría ese auto.
If he were in my place, he wouldn't do this.
Si él estuviese en mi lugar, no haría esto.
If I had more money, I would buy a nice apartment.
Si yo tuviese más dinero, me compraría un lindo apartamento.
If she had more time, she would travel more often.
Si ella tuviera más tiempo, viajaría más a menudo.
If it were not raining, we could go out.
Si no estuviese lloviendo, podríamos salir.
If we didn't have to work today, we could have a picnic.
Si no tuviésemos que trabajar hoy, podríamos tener un picnic.
If they won the lottery, they wouldn't work any more.
Si ellos ganaran la lotería, no trabajarían más.
If I saw her, I would ask her out.
Si la viera, la invitaría a salir.
If you went to Brazil, you wouldn't want to come back.
Si fueras a Brazil, no querrías regresar.
If they spoke spanish, we would understand them.
Si ellos hablasen español, los entenderíamos.
If he didn't live by the river, he couldn't go fishing.
Si el no viviera cerca del río, no podría ir a pescar.
If I didn't want to go, I would tell you.
Si no quisiera ir, te lo diría.
If they worked for that company, they might have better salaries.
Si ellos trabajaran para esa compañía, podrían tener mejores sueldos.
If she wrote a book, it would be a best-seller.
Si ella escribiese un libro, sería un best-seller.