Não te esqueças da maiúscula no início da frase e da minúscula depois da vírgula.

It is a negative command or reminder, addressed to tu.

So the speaker is telling someone:

• Don’t forget the capital letter at the beginning of the sentence
• and the lowercase letter after the comma

In European Portuguese, this is a very natural way to give an instruction.

Because in Portuguese, negative commands use the present subjunctive form.

For the verb esquecer-se with tu:

• affirmative command: esquece-te
• negative command: não te esqueças

So não te esqueças is the correct form for don’t forget when speaking to tu.

A quick comparison:

• Tu esqueces-te = you forget / you are forgetting
• Não te esqueças = don’t forget

So não te esqueces would not work here if you want a command.

Te is the object pronoun used with tu.

The verb here is esquecer-se de, which is a very common way to say to forget.

So:

• esquecer-se de algo = to forget something
• não te esqueças de... = don’t forget...

The te does not usually need a separate translation in natural English, but grammatically it belongs to the verb.

Examples:

• Esqueces-te do livro. = You forget the book.
• Não te esqueças do livro. = Don’t forget the book.

Because não normally forces the pronoun to come before the verb in Portuguese.

So:

• affirmative: Esquece-te
• negative: Não te esqueças

This is a very important pattern in Portuguese. Negation often triggers proclisis, meaning the clitic pronoun moves in front of the verb.

These are contractions, and they are extremely common in Portuguese.

In this sentence:

• da = de + a
• no = em + o

So:

• da maiúscula = de a maiúscula
• no início = em o início

Portuguese normally contracts these combinations.

You can also see:

• da frase = de + a frase
• da minúscula = de + a minúscula
• da vírgula = de + a vírgula

Because the verb pattern is esquecer-se de.

So after esquecer-se, you normally use de:

• esquecer-se de algo
• não te esqueças de algo

That is why the sentence has:

• da maiúscula
• da minúscula

The de comes from the verb, and then it contracts with the feminine article a.

Here they mean:

• maiúscula = capital letter / uppercase letter
• minúscula = lowercase letter

More fully, you could say:

• letra maiúscula
• letra minúscula

But in this sentence, letra is omitted because it is obvious from the context.

So da maiúscula really means something like of the capital letter.

Yes, in this context frase means sentence.

This is a very common false friend for English speakers.

In everyday Portuguese:

• frase often means sentence
• English phrase does not usually translate as frase in grammar explanations

So in this sentence:

• no início da frase = at the beginning of the sentence

If you want the linguistic idea of phrase, Portuguese may use terms like sintagma, depending on the context.

Both início and começo can mean beginning.

But no início da frase sounds especially natural in writing instructions and grammar-related contexts.

So:

• no início da frase = at the beginning of the sentence
• no começo da frase = also possible, but a little less typical in this kind of instruction

Because Portuguese normally repeats the preposition/article combination when linking two parallel elements.

So the structure is:

• não te esqueças da maiúscula...
• e da minúscula...

This sounds balanced and natural.

If you removed the second da, the sentence would sound awkward or incomplete.

It means after the comma.

Breakdown:

• depois de = after
• a vírgula = the comma
• depois da vírgula = after the comma

So the sentence is talking about writing conventions:

• use a capital letter at the beginning of the sentence
• use a lowercase letter after the comma

Yes. With você, the verb and pronoun would change.

A common version would be:

• Não se esqueça da maiúscula no início da frase e da minúscula depois da vírgula.

Compare:

• tu → não te esqueças
• você → não se esqueça

In European Portuguese, tu is very common, but the choice between tu and você depends on region, relationship, and level of formality.