Vimos al amo ayer.

Vimos comes from the verb ver (to see).

Here it is the preterite form for nosotros/nosotras:

• yo vi
• tú viste
• él/ella vio
• nosotros/nosotras vimos
• vosotros/vosotras visteis
• ellos/ellas vieron

So vimos means we saw.

Because Spanish often uses the personal a before a specific human being who is the direct object of the verb.

In this sentence, amo is a person, and he is the one being seen, so Spanish says:

• Vimos al amo

rather than:

• Vimos el amo

That a does not mean to here. It is just the normal marker used before many human direct objects.

It is a contraction of:

• a + el = al

So:

• a el amo is not correct
• al amo is correct

This contraction happens whenever a is followed by the masculine singular article el.

Because with a specific person, Spanish normally requires the personal a.

So:

• Vimos al amo = correct
• Vimos el amo = not correct in standard Spanish for this meaning

A useful way to think about it is:

• el amo = the master / the owner
• al amo = to the master / the owner, but in this kind of sentence the a is grammatical, not really translated as to

Amo can mean master, owner, or male employer, depending on context.

It is not one of the most common everyday words in modern casual Spanish, and in some contexts it can sound:

• old-fashioned
• formal
• linked to social hierarchy
• literary or historical

In many everyday situations, Spanish might use other words such as:

• dueño = owner
• jefe = boss
• señor = gentleman / sir / master in some older contexts

So amo is correct, but its exact feel depends a lot on the situation.

Spanish word order is flexible. Putting ayer at the end is completely natural:

• Vimos al amo ayer

But you could also say:

• Ayer vimos al amo

Both are correct. The difference is mostly about emphasis:

• Vimos al amo ayer = neutral, often answering When did you see him?
• Ayer vimos al amo = puts more focus on yesterday

The preterite is used for a completed action in the past. Seeing someone at a particular time, especially with ayer, is usually treated as a finished event.

So:

• Vimos al amo ayer = We saw the master yesterday
  completed event

If you used the imperfect:

• Veíamos al amo...

that would usually suggest something ongoing, repeated, or backgrounded, such as:

• Veíamos al amo todos los días = We used to see the master every day
• Cuando entramos, veíamos al amo desde la ventana = When we went in, we could see the master from the window

With ayer, the preterite is the normal choice.

Yes. You can say:

• Lo vimos ayer = We saw him yesterday

Here, lo replaces al amo.

Notice that when you use the pronoun, the noun phrase disappears, so the personal a also disappears:

• Vimos al amo ayer
• Lo vimos ayer

By itself, vimos only tells you we saw. The noun al amo tells you who was seen.

If the person has already been mentioned, Spanish often prefers the pronoun:

• Lo vimos ayer

But when the speaker wants to name the person explicitly, they use the noun:

• Vimos al amo ayer

So the sentence is specifically talking about the amo, not just an unspecified him.

Yes, learners often mix them up.

• vimos = we saw
• vemos = we see

The difference is in the vowel:

• vi- in vimos
• ve- in vemos

Also, in most of Spain, v and b are pronounced the same or very similarly, so the important distinction is really the vowel:

• VI-mos
• VE-mos

No, it is not written explicitly, but it is built into the verb vimos.

Spanish often leaves out subject pronouns when the verb form already makes the subject clear.

So:

• Vimos al amo ayer

already means:

• We saw the master yesterday

You could say Nosotros vimos al amo ayer, but that would usually add emphasis:

• We saw the master yesterday

Yes. The article would change.

If it were a feminine noun with la, you would not use a contraction, because a + la stays separate:

• Vimos a la ama ayer

Compare:

• al amo = a + el amo
• a la ama = no contraction

So the contraction only happens with a + el.