Em agosto, a escola envia uma ficha nova e o horário de setembro.

In Portuguese, months are normally written in lowercase, unlike in English. So agosto and setembro are correct.

The same is true for days of the week and seasons:

• segunda-feira
• janeiro
• verão

They are only capitalized if they begin a sentence.

Em is the normal preposition used with months in Portuguese, just like in in English:

• em agosto = in August
• em setembro = in September

You do not normally use an article here, so em agosto is the standard form.

Em agosto is a time expression placed at the beginning of the sentence. The comma helps separate that introductory time phrase from the rest of the sentence.

So this is very similar to English:

• In August, the school sends...

In Portuguese, this comma is common and natural when a time phrase comes first.

Portuguese uses definite articles more often than English. Here, a escola means the school.

In this sentence, the school is treated as a specific, identifiable institution, so the article is natural:

• a escola envia... = the school sends...

Leaving out the article here would sound unnatural in standard Portuguese.

Envia is the present indicative, 3rd person singular, from the verb enviar.

So:

• eu envio = I send
• tu envias
• ele/ela envia = he/she/it sends

In this sentence, the present tense can describe:

• a habitual action
• a scheduled action
• a standard procedure

So it can mean something like the school sends as a regular thing that happens in August.

Ficha is a very flexible word in Portuguese. In school or administrative contexts, it often means something like:

• form
• sheet
• record card
• information sheet

So uma ficha nova probably means a new form or new information sheet, depending on the context.

It does not always have one single fixed English equivalent.

Both are possible, but they can sound slightly different.

• uma ficha nova = a new form, in a straightforward descriptive way
• uma nova ficha = can sound a bit more emphatic, and sometimes more like another/new replacement form

In Portuguese, adjectives often come after the noun in the most neutral, ordinary wording. So ficha nova is the most straightforward choice here.

Horário means schedule or timetable.
De setembro means for/of September in the sense of the September timetable.

So:

• o horário de setembro = the September schedule / the timetable for September

Using de is very natural when naming something by month:

• o horário de setembro
• as aulas de junho
• o relatório de março

De setembro identifies the schedule as the one associated with September, like saying the September timetable.

Para setembro would mean more literally for September, and it can be possible in some contexts, but it is less natural here if you are simply naming the timetable.

So:

• o horário de setembro = the September schedule
• o horário para setembro = a schedule intended for September

The first is the more idiomatic choice in this sentence.

There are two things happening here:

1. Gender

   • ficha is feminine, so it uses uma
   • horário is masculine, so it uses o

2. Definiteness

   • uma ficha nova introduces something as a new form
   • o horário de setembro refers to a more specific thing: the September timetable

So the difference is not random. It reflects both grammatical gender and whether the noun is definite or indefinite.

Yes. Portuguese often avoids repeating the verb when one subject does two things or one subject sends two objects.

So this is perfectly natural:

• a escola envia uma ficha nova e o horário de setembro

It means the school sends both things.

You could repeat the verb, but it would usually sound heavier:

• a escola envia uma ficha nova e envia o horário de setembro

That is grammatical, just less economical unless you want extra emphasis.