Mañana voy a presentar el formulario en la ventanilla.

Both are possible, but they are used a little differently.

• Voy a presentar is the ir a + infinitive future, very common in everyday spoken Spanish.
• Presentaré is the simple future, which can sound a bit more formal, more written, or sometimes less immediate.

In this sentence, Mañana voy a presentar el formulario... sounds very natural in conversation: Tomorrow I’m going to submit/hand in the form...

So:

• Mañana voy a presentar el formulario = very common, conversational
• Mañana presentaré el formulario = also correct, but slightly more formal or less colloquial

In Spanish, many time expressions do not need a preposition.

So you simply say:

• mañana = tomorrow
• hoy = today
• ayer = yesterday

That is different from some other time phrases, where Spanish may use a preposition:

• por la mañana = in the morning
• en mayo = in May
• a las tres = at three o’clock

In your sentence, mañana is just an adverb of time placed at the beginning for context.

Yes, absolutely.

Spanish word order is flexible, especially with adverbs like mañana.

Both are natural:

• Mañana voy a presentar el formulario en la ventanilla.
• Voy a presentar el formulario mañana en la ventanilla.

Starting with mañana puts a little more focus on the time: As for tomorrow, that’s when I’m going to do it.

Because Spanish usually does not need subject pronouns unless they are useful for emphasis, contrast, or clarity.

The verb voy already tells you the subject is I.

• voy = I go / I am going

So:

• (Yo) voy a presentar...

Both are correct, but yo is often omitted.

You would include yo if you wanted emphasis:

• Yo voy a presentar el formulario, no tú.
  I’m the one who is going to submit the form, not you.

Here, presentar means something like:

• to submit
• to hand in
• to file
• sometimes to present

In administrative or official contexts, presentar un formulario often means to submit a form officially.

So this is not necessarily the English present in the sense of giving a talk. It is more about giving a document to an office or institution.

Common examples:

• presentar una solicitud = to submit an application
• presentar un documento = to submit a document
• presentar impuestos = to file taxes

They can overlap, but they are not always identical.

• entregar often means to hand over, to deliver
• presentar often means to submit formally, especially in administrative or official settings

So:

• entregar un trabajo = hand in an assignment
• presentar un formulario = submit a form
• presentar una solicitud = submit an application

In many real situations, both might be understood, but presentar sounds especially appropriate for paperwork and official procedures.

In this context, la ventanilla is the service window, counter window, or desk window in an office, bank, town hall, station, etc.

Literally, ventanilla comes from ventana and means a small window, but in everyday public-administration language it often refers to the window where you speak to a clerk and submit documents.

So en la ventanilla means something like:

• at the counter
• at the service window
• at the clerk’s window

This is a very common word in Spain in offices and public buildings.

Because en is used here to indicate the place where the action happens.

• presentar el formulario en la ventanilla = submit the form at the window/counter

If you say ir a la ventanilla, then a is used because you are expressing movement to that place:

• Voy a la ventanilla = I’m going to the counter/window
• Presento el formulario en la ventanilla = I submit the form at the counter/window

So:

• a = movement toward
• en = location where something happens

Spanish uses definite articles more often than English.

Here:

• el formulario = the form
• la ventanilla = the counter/window

In many practical contexts, Spanish uses the where English might sometimes say a or leave things more general.

For example, if both speaker and listener know which form is being discussed, el formulario is very natural.

Similarly, la ventanilla may refer to the relevant service window in that setting, even if English might say at the counter or at a service window.

So this is normal Spanish usage, not something unusual.

Yes, formulario is a standard and very common word for form, especially official or administrative forms.

Examples:

• rellenar un formulario = fill out a form
• presentar un formulario = submit a form
• firmar un formulario = sign a form

Depending on the context, you may also hear:

• impreso = printed form, official form
• solicitud = application form / application request, depending on context

But formulario is perfectly normal and easy to understand.

Not naturally in this context.

Although presentar can mean to present or to introduce in other situations, the combination of:

• presentar
• el formulario
• en la ventanilla

strongly points to an administrative meaning: to submit/hand in the form at the counter.

So context is doing a lot of work here. With paperwork and an office window, the meaning is clearly about submission, not introduction.

In standard Spain Spanish, a simple approximation is:

• ben-ta-NEE-ya

A few useful pronunciation points:

• v in Spanish sounds very similar to b for most speakers.
• ll in most modern Spanish is pronounced like y in English yes.
• The stress is on -ni-: ventanilla

So:

• ven-ta-NI-lla
  approximately ben-ta-NEE-ya

Yes, very naturally.

This sounds like something someone might say when talking about:

• a town hall
• a government office
• a bank
• an administrative office
• a transport office
• any place with a service counter/window

Because of formulario and ventanilla, the sentence has a very practical, bureaucratic, everyday Spain feel. It sounds like normal real-life Spanish.