Quando volto para casa, guardo a mochila, limpo o mouse e desligo o computador.

Portuguese often leaves out subject pronouns when the verb ending already shows who the subject is.
Here, volto clearly means I return / I come back, so eu is optional.

You could say Quando eu volto para casa, but Quando volto para casa sounds very natural and normal.

They are all first-person singular present indicative forms:

• volto = I return / I come back
• guardo = I put away / I store / I keep
• limpo = I clean
• desligo = I turn off

So the whole sentence keeps the same subject throughout: I do all of these actions.

In Portuguese, just like in English, the present tense can describe a habit or routine.
So Quando volto para casa... means something like Whenever I get home... or When I come home...

It is not talking about one specific future event. It is describing what the speaker عادة does.

Then Portuguese usually uses the future subjunctive after quando:

• Quando eu voltar para casa, vou guardar a mochila...

That means When I get back home, I will put away the backpack...

So:

• Quando volto para casa... = habitual / repeated action
• Quando eu voltar para casa... = a future occasion

When casa means home, Portuguese often uses it without an article:

• vou para casa
• chego em casa
• volto para casa

But if you mean a specific house/building, you usually use the article:

• volto para a casa da minha mãe

So in this sentence, para casa means home, not just any house.

Not usually in this kind of sentence. This is a classic false friend.

Here, guardar means to put away, to store, to keep, or to put in its place.

So guardo a mochila is more like:

• I put away the backpack
• I store the backpack

It does not usually mean I guard the backpack in the English sense.

Portuguese uses definite articles much more often than English does.
When talking about specific, known objects, the article is very natural:

• guardo a mochila
• limpo o mouse
• desligo o computador

In English, we might sometimes omit the article in similar routine contexts, but in Portuguese the article usually stays.

Yes, mouse is very commonly used in Brazilian Portuguese for the computer device.
It normally takes the masculine article: o mouse.

Many borrowed technology words in Portuguese become masculine by default, especially when there is no strong reason to make them feminine.

Here it is a verb: I clean.

That can confuse learners because limpo can also be an adjective meaning clean:

• O mouse está limpo = The mouse is clean

In your sentence, it is clearly a verb because it is part of a list of actions:

• guardo, limpo, desligo

For devices and machines, desligar is the normal verb for to turn off or to shut down:

• desligo o computador
• desligo a televisão

Apagar is more commonly used for lights:

• apago a luz

So desligo o computador is the most natural choice here.

There are two reasons:

1. Quando volto para casa is an introductory time clause, so it is separated from the main part of the sentence with a comma.
2. The rest is a list of actions, so commas separate the items:

• guardo a mochila
• limpo o mouse
• e desligo o computador

Just like in English, there is normally no comma before the final e in a simple list.

Yes. In Brazilian Portuguese, pra is a very common informal spoken form of para.

So Quando volto pra casa... sounds very natural in conversation.
In more neutral or careful writing, para is usually preferred.