Mi padre va a atornillar la balda otra vez porque uno de los tornillos se ha aflojado.

Ir a + infinitive is a very common way to talk about the near future or an intended action in everyday Spanish.

• Mi padre va a atornillar... = my father is going to screw/fix...
• Mi padre atornillará... = my father will screw/fix...

In conversation, va a atornillar sounds more natural and immediate. The simple future is possible, but it can sound more formal, more predictive, or less conversational.

It is part of the fixed future structure ir a + infinitive.

So:

• va = he goes / he is going
• a atornillar = to screw / to fasten with screws

Together, va a atornillar means is going to fasten/screw.

You should learn this as one pattern: ir a + infinitive = to be going to + verb

Yes, it could.

Spanish often drops subject pronouns and even noun subjects when the context is clear. So:

• Mi padre va a atornillar la balda...
• Va a atornillar la balda...

Both are possible.

Including mi padre makes the subject explicit. It may be used because:

• the speaker wants to clarify who will do it
• the sentence is starting a new idea
• there is a slight emphasis on my father

Atornillar means to fasten with a screw / to screw in / to attach using screws.

In this sentence, it suggests that the shelf board will be secured again with a screw or screws.

A useful contrast:

• atornillar = to screw/fasten with screws
• apretar = to tighten

So if you only mean tighten the screw, Spanish might also say apretar el tornillo. But atornillar la balda focuses more on fastening the shelf itself.

Yes. In Spain, balda commonly means a shelf board: the horizontal piece of wood or other material that forms a shelf.

It is slightly more specific than some other words:

• balda = the actual shelf board/plank
• estante = a shelf, or sometimes shelving/shelf unit
• repisa = a ledge or small shelf

So la balda here is specifically the board that needs fastening again.

Yes, both are possible.

• otra vez = again
• de nuevo = again / anew

In everyday speech, otra vez is extremely common and natural. De nuevo is also correct, sometimes a little more neutral or slightly more formal depending on context.

So these both work:

• Mi padre va a atornillar la balda otra vez
• Mi padre va a atornillar la balda de nuevo

Because porque is the conjunction meaning because.

Compare:

• porque = because
• por qué = why? / for what reason?
• el porqué = the reason, the why
• por que = a less common combination in other structures

Here the sentence gives a reason, so porque is the correct form: ...porque uno de los tornillos se ha aflojado.

Because uno de... is the normal structure for one of...

• uno de los tornillos = one of the screws
• una de las piezas = one of the pieces

Here uno is being used as a pronoun meaning one, not just as the indefinite article un.

So:

• un tornillo = a screw
• uno de los tornillos = one of the screws

Because the true subject is uno, not los tornillos.

So the structure is:

• uno = the subject
• de los tornillos = a phrase telling you what group that one belongs to

That is why the verb is singular:

• Uno de los tornillos se ha aflojado.
• not Uno de los tornillos se han aflojado.

This is the same idea as in English: One of the screws has come loose, not have come loose.

Because aflojarse here means to come loose / to become loose.

This is different from transitive aflojar, which means to loosen something.

Compare:

• He aflojado el tornillo. = I have loosened the screw.
• El tornillo se ha aflojado. = The screw has come loose.

So the se shows a change of state affecting the screw itself. It is not really a literal reflexive idea like the screw loosened itself in a conscious sense. It is just how Spanish expresses became loose / came loose.

Both are possible, but in Spain the present perfect is very often used for a recent past event that still matters now.

So in Spain:

• se ha aflojado often sounds natural for has come loose
• especially when the result is still relevant now

That fits this sentence perfectly: the screw has come loose, so the father is going to fix the shelf again.

In much of Latin America, many speakers would more naturally use the preterite: uno de los tornillos se aflojó.

Spanish uses the definite article very often when talking about specific things already identifiable in the situation.

Here:

• la balda = the shelf board we both know about
• los tornillos = the screws belonging to that shelf or involved in that situation

So even though English might sometimes say a shelf or omit some articles differently, Spanish naturally uses la and los because these are specific, known objects in context.