Uso un tono informal cuando hablo con mis amigos.

Because Spanish often drops subject pronouns when the verb already makes the subject clear.

• uso = I use
• The -o ending tells you the subject is I, so yo is not necessary.

You could say Yo uso un tono informal... if you want extra emphasis or contrast, but in normal speech, uso by itself is more natural.

Uso is the first-person singular present tense form of the verb usar.

• usar = to use
• uso = I use

This is the regular present tense pattern for -ar verbs:

• hablo = I speak
• trabajo = I work
• uso = I use

In Spanish, singular countable nouns usually need an article or determiner.

So tono normally needs something like:

• un tono = an informal tone / one informal tone
• el tono = the tone
• mi tono = my tone

Just saying uso tono informal would sound incomplete in standard Spanish. Un tono informal is the natural way to say it.

Here, tono means tone, as in the way someone speaks.

It does not just refer to sound or pitch. It can also mean:

• style of speaking
• level of formality
• attitude in speech

So un tono informal means someone speaks in a casual, relaxed, non-formal way.

Because this sentence talks about a habitual or repeated action, not a future event.

• cuando hablo con mis amigos = when I speak with my friends / whenever I talk with my friends

Spanish often uses the present indicative after cuando for things that happen regularly.

You would use cuando hable more for a future idea, such as:

• Cuando hable con mis amigos, les contaré la noticia. = When I speak to my friends, I’ll tell them the news.

So in your sentence, hablo is correct because it describes a general habit.

Because Spanish uses the present tense very naturally for general truths, routines, and habits.

This sentence is basically saying:

• Whenever I talk with my friends, I use an informal tone.

That is a regular pattern, so the present tense fits perfectly.

English does something similar with When I talk to my friends..., so the Spanish structure is very close here.

Because the verb hablar commonly uses con to mean to speak with someone.

• hablar con alguien = to talk with someone

Examples:

• Hablo con mi mamá. = I talk with my mom.
• Hablas con tus compañeros. = You talk with your classmates.

You may also see hablar a alguien or hablarle a alguien, but that often emphasizes speaking to someone rather than having a mutual conversation. In this sentence, con is the most natural choice.

Because in Spanish, possessive adjectives like mi, mis, tu, tus usually replace the article.

So you say:

• mis amigos = my friends
• not los mis amigos

This is different from some other languages, but it is standard in Spanish.

Compare:

• los amigos = the friends
• mis amigos = my friends

Not necessarily. In Spanish, the masculine plural can refer to:

• a group of all males, or
• a mixed-gender group

So mis amigos could mean:

• my male friends
• my friends in general, if the group includes males
• sometimes just my friends, without focusing on gender

If the group is all female, you would say mis amigas.

Yes, absolutely. That version is completely natural.

Both are correct:

• Uso un tono informal cuando hablo con mis amigos.
• Cuando hablo con mis amigos, uso un tono informal.

The difference is mostly about emphasis:

• starting with Uso un tono informal... puts the focus first on what I do
• starting with Cuando hablo con mis amigos... puts the focus first on the situation

In speech and writing, both are common.

Usually, no—not for this meaning.

Uso expresses a general habit:

• I use an informal tone when I talk with my friends.

Estoy usando would sound more like something happening right now at this moment:

• I am using an informal tone.

Since the sentence describes a usual pattern, the simple present uso is the natural choice.

Yes, pretty much. Informal in Spanish is very similar to English informal.

In this sentence, it refers to a casual, relaxed way of speaking, especially with friends.

For example:

• lenguaje informal = informal language
• tono informal = informal tone
• registro informal = informal register

So this is a very transparent vocabulary item for English speakers.