I forgot to
Compré una linterna, pero me olvidé de comprar las pilas.
I bought a flashlight, but I forgot to buy the batteries.
Me olvidé de cerrar las cortinas.
I forgot to close the curtains.
I almost forgot about all that.
Me olvidé de cortar las uñas de mi perro.
I forgot to trim my dog's nails.
I forgot to call you.
I didn't forget about you all.
I forgot to ask him.