vs
QUICK ANSWER
"At last" is a phrase which is often translated as "por fin", and "last" is an adjective which is often translated as "último". Learn more about the difference between "at last" and "last" below.
at last( 
aht
lahst
)A phrase is a group of words commonly used together (e.g., once upon a time).
1. (finally)
a. por fin 
After driving for 10 hours without stopping, we arrived to Texas at last.Después de manejar por 10 horas sin parar, por fin llegamos a Texas.
b. finalmente 
And, at last, we will be able to hear from our president.Y, finalmente, podremos escuchar a nuestro presidente.
c. al fin 
My kids are all at school, and at last there is peace in my house.Mis hijos están en la escuela, y al fin hay paz en mi casa.
last(
lahst
)An adjective is a word that describes a noun (e.g., the big dog).
1. (final)
a.  no direct translation
This refers to an idiomatic word or phrase for which there is no word-for-word translation.
She's the last person I want to see right now.Ella es la última persona a la que quiero ver ahora.
That was the last thing I thought would happen.Era lo que menos pensaba que pasaría.
A noun is a word referring to a person, animal, place, thing, feeling, or idea (e.g., man, dog, house).
a. el último (M), la última (F)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
(f) means that a noun is feminine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
The youngest child is usually the last to leave home.El hijo menor es normalmente el último en irse de casa.
a.  no direct translation
This refers to an idiomatic word or phrase for which there is no word-for-word translation.
I'm making a sandwich with the last of a jar of peanut butter.Me estoy haciendo un bocadillo con lo que queda de un tarro de mantequilla de maní.
This is the last I will smoke before quitting tobacco.Este es el último que me fumaré antes de dejar el tabaco.
a.  no direct translation
This refers to an idiomatic word or phrase for which there is no word-for-word translation.
I went to the dentist the day before last.Fui al dentista anteayer.
The next course is more interesting than the last.El siguiente curso es más interesante que el anterior.
An adverb is a word that describes a verb, an adjective, or other adverbs (e.g., to run quickly, very tired).
7. (at the end)
8. (finally)
a. por último 
And last of all, cover it with chocolate chips.Y, por último, cúbralo de trocitos de chocolate.
An intransitive verb is one that does not require a direct object (e.g., The man sneezed.).
10. (to continue)
a. durar 
This blender is made to last for a lifetime.Esta batidora está fabricada para durar toda una vida.
12. (to be enough)
a. durar 
We have enough bread to last a couple of days.Tenemos bastante pan para durar un par de días.
13. (to survive)
a. durar 
The patient won't last much longer; his disease is advanced.El paciente no durará mucho, su enfermedad está avanzada.
A transitive verb is a verb that requires a direct object (e.g., I bought a book.).
14. (to continue)