Si tu fais une erreur, recommence calmement.

This is a very common French pattern:

• Si + present = the condition
• imperative = the instruction or result

So:

• Si tu fais une erreur = If you make a mistake
• recommence calmement = start again calmly

French often uses this pattern for advice, instructions, and warnings:

• Si tu es fatigué, repose-toi. = If you’re tired, rest.
• Si tu ne comprends pas, demande. = If you don’t understand, ask.

So even though English might sometimes use other structures, this French pattern is completely normal.

Because fais is the correct present tense form of faire with tu.

The present tense of faire is:

• je fais
• tu fais
• il/elle/on fait
• nous faisons
• vous faites
• ils/elles font

So:

• tu fais = you do / you make
• il fait = he does / he makes

Since the sentence says si tu fais une erreur, it needs the tu form: fais.

Because recommence is in the imperative, which is the form used for commands or instructions.

In French, imperative forms usually do not include the subject pronoun.

So instead of saying:

• Tu recommences. = You start again.

you say:

• Recommence ! = Start again!

For recommencer, the imperative forms are:

• recommence = start again (to one person, informal)
• recommençons = let’s start again
• recommencez = start again (formal or plural)

So recommence calmement is a command addressed to tu.

In French, you usually need an article before a singular countable noun.

Erreur is a countable noun, so French normally says:

• une erreur = a mistake
• l’erreur = the mistake
• cette erreur = this mistake

English often allows a bare noun less easily in this kind of sentence, and French generally requires the article even more strongly.

So:

• Si tu fais une erreur = If you make a mistake

That sounds natural and complete in French.

Here, recommence means start again or do it again from the beginning.

It comes from recommencer, which means to begin again.

So it is not the same as:

• continue = keep going
• essaie = try
• réessaie = try again

There is a slight nuance:

• recommence suggests beginning the action again
• réessaie suggests making another attempt

In many contexts, both could work, but recommence calmement gives the idea of starting over calmly after a mistake.

Calmement is an adverb meaning calmly.

In French, adverbs often come after the verb, especially in straightforward sentences like this one.

So:

• Recommence calmement. = Start again calmly.

That word order is very natural in French.

You could sometimes move adverbs around for emphasis in other contexts, but here the most normal placement is after the verb.

Tu is the informal singular form of you.

So this sentence is speaking to:

• one person
• in an informal way

If you wanted to address someone formally, or several people, you would use vous:

• Si vous faites une erreur, recommencez calmement.

So the original sentence sounds like advice to one person in a friendly, familiar, or instructional context.

The comma is standard and helpful here because it separates:

• the condition: Si tu fais une erreur
• the main instruction: recommence calmement

French usually writes this type of sentence with a comma when the si-clause comes first.

So this is the normal punctuation:

• Si tu fais une erreur, recommence calmement.

If you reverse the order, the comma is often not used the same way:

• Recommence calmement si tu fais une erreur.

Both are possible, but the original version is very natural for instructions.

Recommence is pronounced approximately like ruh-ko-mons in standard French, though English spelling can only approximate it.

A few useful points:

• the first re- is often pronounced like a light ruh
• commence sounds roughly like ko-mons
• the final -e is not pronounced

So the whole word is approximately:

• recommence → ruh-ko-mons

Also, calmement is pronounced roughly kalm-mon, with the ending sounding nasal rather than fully pronounced like English ment.

Yes. That would mean:

• Si tu fais des erreurs, recommence calmement. = If you make mistakes, start again calmly.

The difference is:

• une erreur = a mistake / one mistake / any single mistake
• des erreurs = mistakes in general, more than one or as a general possibility

The original sentence with une erreur sounds very natural because it refers to the situation if you make a mistake. It presents the mistake as a single possible event.