Mi madre desconfía de ese anuncio, pero yo creo que la oferta es real.

Because desconfiar normally takes the preposition de in Spanish: desconfiar de algo/alguien = to distrust / be suspicious of something or someone.

So:

• desconfía de ese anuncio = she distrusts / is suspicious of that advert

This is just part of the verb’s pattern, so it has to be learned together with the verb:

• confiar en = to trust in
• desconfiar de = to distrust / be suspicious of

English learners often want to translate word for word, but here the preposition does not match English neatly.

Because the subject is mi madre, which is she.

The verb desconfiar is in the present tense:

• yo desconfío = I distrust
• tú desconfías = you distrust
• él/ella desconfía = he/she distrusts

Since mi madre = she, the correct form is desconfía.

The accent mark shows where the stress goes: des-con-FÍ-a.

It also helps show that í and a are pronounced in separate syllables, not blended into one. So desconfía has four syllables:

• des
• con
• fí
• a

Without the accent, Spanish spelling rules would suggest a different stress pattern.

Yes, pero creo que la oferta es real would also be correct.

Spanish often omits subject pronouns because the verb ending already shows who the subject is. Here, creo already means I believe / I think.

Adding yo gives extra emphasis or contrast. In this sentence, that makes sense because there is a contrast:

• Mi madre desconfía...
• pero yo creo...

So yo highlights the difference between the mother’s opinion and the speaker’s opinion: but I think...

Ese means that, while este means this.

Spanish has a three-way distinction:

• este = this, near the speaker
• ese = that, near the listener or not especially near the speaker
• aquel = that over there, farther away

In many everyday situations, ese is the normal way to say that. So ese anuncio simply means that advert/ad.

They are related, but they are not the same thing.

• anuncio = advert, advertisement, ad
• oferta = offer, deal, special promotion

So the sentence is talking about:

• the mother distrusting the advert
• the speaker believing the offer/deal mentioned in that advert is real

In other words, the ad contains an offer, and the speaker thinks that offer is genuine.

Spanish uses articles more often than English does.

Here, la oferta refers to a specific offer, probably the one mentioned in ese anuncio. So Spanish naturally uses the definite article:

• la oferta es real

Even where English might sometimes say the offer or sometimes just the offer is real, Spanish strongly prefers the article in this kind of sentence.

Because real here describes an essential quality: the offer is genuine, not fake.

Spanish generally uses:

• ser for identity, defining characteristics, and what something is
• estar for states, conditions, and location

So:

• la oferta es real = the offer is real/genuine

Using estar with real would sound wrong in this context.

Because creer que is the normal structure for saying to think/believe that...

So:

• creo que la oferta es real = I think that the offer is real

In English, that is often optional: I think the offer is real. In Spanish, que is normally required here.

The given word order is the most natural:

• Mi madre desconfía de ese anuncio, pero yo creo que la oferta es real.

Spanish word order is fairly flexible, but not completely free. You could move things around for emphasis, but the basic order here is standard and clear:

• subject + verb + complement
• Mi madre
  • desconfía
    • de ese anuncio
• yo
  • creo
    • que la oferta es real

A version like De ese anuncio desconfía mi madre is possible, but it sounds more marked or literary because it emphasizes de ese anuncio.

Yes, if the tone is more personal or informal.

Compare:

• Mi madre desconfía de ese anuncio = my mother distrusts that advert
• Mamá desconfía de ese anuncio = Mum/Mom distrusts that advert

In Spain, mamá is common in everyday speech when talking about your own mother. Mi madre sounds a bit more neutral and descriptive.

A careful pronunciation would be roughly:

Mi MA-dre des-con-FÍ-a de E-se a-NUN-cio, PE-ro yo CRE-o ke la o-FER-ta es re-AL.

A few useful notes:

• desconfía is stressed on fí
• creo has two vowel sounds: CRE-o
• in much of Spain, c before i in anuncio is pronounced like the th in thin
• real is usually two syllables: re-AL

So in much of Spain, anuncio sounds approximately like a-NOON-thyo.

The whole sentence is in the present indicative:

• desconfía
• creo
• es

This tense is used because the speaker is talking about current opinions and beliefs:

• the mother is suspicious now
• the speaker believes now
• the offer is considered real now

It is a very common tense for stating opinions, facts, and present situations.