A luglio preferisco restare in ombra, ma ad agosto vado comunque al lago con mia sorella.

With months, Italian often uses a where English uses in.

• a luglio = in July
• ad agosto = in August

So you should not translate the preposition word-for-word. This is just the normal Italian pattern in expressions like these.

You may also hear month expressions without a preposition in some contexts, but a + month is very common and natural.

Ad is just a with an extra d added before a vowel for smoother pronunciation.

• a luglio
• ad agosto

This extra d is especially common before words beginning with a. It helps avoid the awkward sequence a agosto. In modern Italian, this is a normal and natural choice here.

After preferire, if another action follows, Italian uses the infinitive.

• preferisco restare = I prefer to stay
• not preferisco resto

This is like English I prefer to stay, not I prefer I stay.

Other examples:

• preferisco mangiare a casa
• preferiamo partire domani

So in your sentence, restare stays in the infinitive because it depends on preferisco.

Both can often be translated as to stay, but there is a slight nuance.

• restare suggests remaining in a place or condition
• stare is more general and often means to be or to stay

So:

• preferisco restare in ombra feels like I prefer to remain in the shade
• preferisco stare in ombra also works and sounds natural, but it can feel a little less focused on the idea of remaining there

In many everyday situations, the two are very close in meaning.

Yes, both are possible in Italian, but they are not always exactly the same.

• in ombra means in the shade, focusing on being out of direct sunlight
• all'ombra often suggests being under the shade of something, such as a tree or a building

In this sentence, restare in ombra sounds like a general preference for staying out of the sun. That is why it works very well.

Also, stare/restare in ombra is a very common expression.

Comunque means something like:

• anyway
• still
• all the same
• in any case

In this sentence, it shows contrast:

• In July, the speaker prefers to stay in the shade
• But in August, the speaker still goes to the lake anyway

So comunque adds the idea that, despite the preference for shade, the trip to the lake still happens.

Yes, comunque is fairly flexible.

In your sentence:

• vado comunque al lago

This is very natural.

You could also hear:

• comunque vado al lago
• vado al lago comunque

The exact position can slightly change the rhythm or emphasis, but the overall meaning stays very similar. In your sentence, placing comunque after the verb sounds smooth and standard.

Al is the contraction of a + il.

• a + il = al

So:

• vado al lago literally breaks down as I go to the lake

But in natural usage, andare al lago often means going to the lake area, lakeside, or a place by the lake, not necessarily into the water itself.

This is similar to other Italian place expressions:

• andare al mare
• andare al parco
• andare al ristorante

In standard Italian, singular close family members usually take a possessive without the article.

So you say:

• mia sorella
• mio fratello
• mia madre
• mio padre

That is why the sentence has con mia sorella.

A few useful notes:

• With plurals, the article usually comes back: i miei fratelli
• If the family noun is modified, the article often appears: la mia sorella maggiore
• With non-family nouns, the article is normally used: la mia amica

Yes. That would also be correct and natural.

The difference is mainly one of nuance:

• stare in ombra = to stay/be in the shade
• restare in ombra = to remain in the shade

So restare can sound a bit more like continuing in that condition, while stare is a little more neutral. In everyday speech, both are very common.

In Italian, names of months are normally written with a lowercase letter.

So:

• luglio
• agosto
• gennaio
• dicembre

This is different from English, where month names are capitalized. In Italian, you only capitalize them if they begin the sentence or are part of a title that requires capitalization.