Não tenha vergonha de perguntar quando não entender a lição.

Because this is a negative command: Don’t be ashamed...

In Brazilian Portuguese, negative commands for você use the present subjunctive form:

• ter → tenha
• so não tenha = don’t have / don’t be

Also, ter vergonha is a fixed expression meaning to be ashamed or to feel embarrassed.

So:

• Não tenha vergonha = Don’t be ashamed / Don’t feel embarrassed

If you said não tem, that would usually be interpreted as a statement like doesn’t have, not a command.

Yes, the subject is omitted, but it is understood as você.

Portuguese often leaves out the subject when the verb form makes it clear enough or when context does.

So this sentence is really:

• (Você) não tenha vergonha de perguntar...

In Brazil, this is a very common way to address someone directly in a neutral, everyday way.

Because ter vergonha is an idiomatic expression.

Literally, it is to have shame, but in natural English the meaning is:

• to be ashamed
• to feel embarrassed

This happens a lot between languages: the literal words do not always match the natural translation.

Some related examples:

• ter medo = to be afraid
• ter fome = to be hungry
• ter razão = to be right

So ter often appears in expressions that English translates with to be.

Because Portuguese uses the pattern:

• ter vergonha de + infinitive

So:

• ter vergonha de perguntar = to be ashamed to ask
• ter vergonha de falar = to be ashamed to speak
• ter vergonha de errar = to be ashamed to make mistakes

The preposition de is required by the expression. It links vergonha to the action that causes the shame or embarrassment.

Because after de, Portuguese uses the infinitive.

Here the structure is:

• não tenha vergonha de perguntar
• literally: don’t have shame of asking

So perguntar is not another command here. It is the action connected to vergonha.

If you used pergunte, that would be a separate command:

• Não tenha vergonha. Pergunte.
• Don’t be shy. Ask.

That is possible, but it is a different sentence structure.

Because the sentence contains two separate negatives, and each one negates a different verb.

• Não tenha vergonha = Don’t be ashamed
• quando não entender a lição = when you don’t understand the lesson

So the first não applies to tenha, and the second não applies to entender.

In English we do the same thing:

• Don’t be ashamed to ask when you don’t understand the lesson.

Because after quando, Portuguese often uses the future subjunctive when talking about a future or possible situation.

This sentence is giving advice about what to do whenever that situation happens in the future:

• when you don’t understand the lesson

For the verb entender, the future subjunctive form is:

• entender

That looks exactly like the infinitive, which can be confusing.

So here entender is not just an infinitive sitting there by itself; it is functioning as the future subjunctive:

• quando eu entender
• quando você entender
• quando eles entenderem

By contrast:

• quando não entende sounds more like a habitual present statement, depending on context.
• quando não entender fits the advice/command style very well.

Because of the structure quando + verb.

After quando, if Portuguese is referring to a future or uncertain event, it commonly uses the future subjunctive.

So in:

• quando não entender a lição

the verb is understood as:

• when you do not understand / when you happen not to understand

With many regular verbs, the future subjunctive looks identical to the infinitive:

• falar
• comer
• partir
• entender

That is why it can be hard for learners to spot.

A clearer example is an irregular verb:

• quando for = when you go / when it is
• quando vier = when you come
• quando tiver = when you have

Those forms make it easier to see that Portuguese is not using an infinitive there.

Both can work, but they give slightly different nuances.

• quando = when / whenever
• se = if

In this sentence, quando suggests that not understanding something is a normal situation that may come up:

• Ask when you don’t understand
• almost like whenever that happens

If you said:

• Não tenha vergonha de perguntar se não entender a lição

that would also be correct, but it sounds a bit more purely conditional:

• if you don’t understand the lesson

So quando feels natural and encouraging here.

Not exactly.

• lição usually means lesson, exercise, or the material being learned
• aula usually means class, lesson period, or the actual class session

So:

• não entender a lição = not understand the lesson/content
• não entender a aula = not understand the class / what is being explained in class

Depending on context, lição can refer to:

• a school lesson
• homework
• a unit of learning
• the content being taught

Because Portuguese uses definite articles very naturally with nouns, often more often than English does.

Here a lição means:

• the lesson
• the specific lesson being discussed or studied

English sometimes drops the article where Portuguese keeps it, but in Portuguese this sounds completely normal.

So:

• entender a lição = understand the lesson

It is neutral and very common in Brazilian Portuguese.

The form tenha points to the você style, which is the normal everyday way of speaking in much of Brazil.

So the tone is:

• polite
• natural
• encouraging

It is not overly formal, but it is not slangy either.

If you changed the person, the sentence would change too:

• tu: Não tenhas vergonha de perguntar quando não entenderes a lição.
• vocês: Não tenham vergonha de perguntar quando não entenderem a lição.

In Brazil, the você version is usually the most broadly useful one for learners.

Yes. Both are natural.

• perguntar = to ask
• fazer perguntas = to ask questions

So you could say:

• Não tenha vergonha de perguntar...
• Não tenha vergonha de fazer perguntas...

The first is shorter and more direct. The second emphasizes questions a little more.

Both sound good in Brazilian Portuguese.