Al matí m'agrada menjar torrades amb mantega i melmelada.

Al matí means in the morning.

Grammatically, al is the contraction of a + el. So literally it is something like at the morning, but the natural English translation is in the morning.

This pattern is very common in Catalan with times of day:

• al matí = in the morning
• a la tarda = in the afternoon
• a la nit = at night

In this sentence, it most naturally sounds general/habitual: in the morning or in the mornings.

Because the sentence is about a preference — m'agrada = I like — the idea is usually:

• In the morning, I like to eat...

If you wanted to mean this morning, Catalan would normally say:

• aquest matí = this morning

The apostrophe shows that em has been shortened before a vowel.

So:

• em agrada becomes m'agrada

Here, em means to me.

Catalan often does this with weak pronouns before vowels:

• m'agrada = em agrada
• t'agrada = et agrada
• l'escolto = el/la escolto, with the usual contractions depending on the pronoun

Because agradar does not work like English to like.

Catalan agradar works more like:

• to be pleasing to

So m'agrada menjar torrades... is literally closer to:

• Eating toast with butter and jam is pleasing to me

That is why:

• m' = to me
• agrada agrees with the thing that is pleasing, not with I

So you say:

• M'agrada = I like it / It pleases me not
• M'agrado = I please myself

Because the grammatical subject here is not just torrades.

The subject is the whole infinitive phrase:

• menjar torrades amb mantega i melmelada = eating toast with butter and jam

An infinitive phrase like menjar... behaves as a singular idea, so Catalan uses:

• agrada = singular

Compare:

• M'agrada menjar torrades. = I like eating toast.
• M'agraden les torrades. = I like toast / I like slices of toast.

In the second sentence, les torrades is the subject, and it is plural, so the verb becomes agraden.

After agradar, if you want to say like doing something, Catalan uses the infinitive.

So:

• m'agrada menjar = I like to eat / I like eating

But:

• menjo means I eat

That would not fit after m'agrada in this structure.

Compare:

• Menjo torrades al matí. = I eat toast in the morning.
• M'agrada menjar torrades al matí. = I like eating toast in the morning.

Yes, often it does.

In Catalan, torrada usually means a slice/piece of toast or toasted bread, so the plural torrades is very natural when talking about breakfast.

So:

• una torrada = a piece/slice of toast
• torrades = toast, toasted slices, pieces of toast

English often treats toast as uncountable, but Catalan commonly uses the countable form.

Because they are being used in a general, nonspecific way.

So:

• amb mantega i melmelada = with butter and jam

Catalan often leaves out the article in this kind of food description, especially after a preposition like amb.

If you were talking about specific butter or specific jam, articles would be more likely:

• amb la mantega i la melmelada de casa = with the butter and the homemade jam

But in a general breakfast sense, amb mantega i melmelada sounds perfectly natural.

They are close in meaning, but the focus is different.

• M'agrada menjar torrades...
  = I like eating toast...
  This focuses on the activity of eating.

• M'agraden les torrades...
  = I like toast...
  This focuses on the food itself.

There is also a grammar difference:

• agrada because menjar torrades... is a singular infinitive phrase
• agraden because les torrades is a plural noun phrase

Yes. That is also correct.

Catalan allows some flexibility with time expressions like al matí.

• Al matí m'agrada menjar torrades...
  puts in the morning first, setting the scene

• M'agrada menjar torrades... al matí
  sounds a bit more neutral and leaves the time until the end

Both are natural. The difference is mainly one of focus and rhythm, not basic meaning.

Yes. Amb is the standard Catalan word for with.

So:

• torrades amb mantega = toast with butter
• cafè amb llet = coffee with milk

In this sentence, amb mantega i melmelada tells you what goes with the toast.

For most learners, translating melmelada as jam is the safest choice.

It refers to fruit spread/preserve, and in everyday use that is usually the right English equivalent here.

So:

• mantega i melmelada = butter and jam

Depending on context, English might sometimes use preserve or marmalade for certain kinds, but jam is the normal translation in a sentence like this.