Es mejor que pongas el intermitente antes de girar a la izquierda.

Because es mejor que normally triggers the subjunctive in Spanish.

In this sentence, the speaker is giving a recommendation or judgment about what someone should do, not simply stating a fact. That is why Spanish uses:

• Es mejor que pongas... = It’s better that you put/use...

If you used pones, that would be the indicative, and it would sound wrong here.

A useful pattern to remember is:

• Es mejor que + subjunctive
• Es importante que + subjunctive
• Es bueno que + subjunctive

So:

• Es mejor que pongas el intermitente...
• not Es mejor que pones...

Pongas is the present subjunctive, tú form, of poner.

The present subjunctive of poner is:

• yo: ponga
• tú: pongas
• él/ella/usted: ponga
• nosotros/as: pongamos
• vosotros/as: pongáis
• ellos/ellas/ustedes: pongan

So in this sentence, the implied subject is tú:

• Es mejor que (tú) pongas...

Notice that poner is irregular because of the pong- stem in the subjunctive.

Because Spanish often leaves out subject pronouns when the verb form already shows who the subject is.

Here, pongas already tells you the subject is tú, so tú is unnecessary unless you want emphasis or contrast.

So these mean the same thing:

• Es mejor que pongas el intermitente...
• Es mejor que tú pongas el intermitente...

The second one sounds more emphatic, as if contrasting with someone else.

Yes, absolutely.

Both are correct, but they are slightly different in feel:

• Es mejor que pongas el intermitente...
  = direct advice to you
• Es mejor poner el intermitente...
  = a more general statement, like a rule or recommendation

So:

• Es mejor que pongas... sounds more personal.
• Es mejor poner... sounds more general and impersonal.

Both are very natural.

Because when the subject stays the same, Spanish usually uses:

• antes de + infinitive

Here, the person who puts on the indicator is the same person who turns left, so Spanish uses the infinitive:

• antes de girar

If the subject changes, then Spanish uses:

• antes de que + subjunctive

For example:

• Pon el intermitente antes de que el coche gire.
  = Use the indicator before the car turns.

So in your sentence:

• same subject → antes de girar
• different subject → antes de que + subjunctive

Because in Spanish, the normal expression is:

• girar a la izquierda
• girar a la derecha

This is just the standard preposition used with directions after verbs like girar or doblar.

Examples:

• Gira a la izquierda.
• Gira a la derecha.

You can think of it as a fixed expression meaning turn left/right.

In Spain, el intermitente is the normal everyday word for a car’s turn signal / indicator.

In other Spanish-speaking countries, other words may be more common, such as:

• la direccional
• la luz de giro
• el indicador

So if you are learning Spanish from Spain, el intermitente is exactly the word you should know.

Also, in Spain, people commonly say:

• poner el intermitente = to indicate / to put the turn signal on

Yes. In Spain, poner el intermitente is very natural and common.

Literally, poner means to put, but in many everyday expressions it works more like turn on / use.

So:

• poner el intermitente = turn on the indicator / signal
• poner la luz = turn on the light
• poner la radio = turn on the radio

You may also hear other expressions, such as:

• señalizar
• indicar
• poner el indicador

But poner el intermitente is extremely idiomatic in Spain.

In normal use, yes: es mejor que is followed by the subjunctive.

That is because it expresses an evaluation, recommendation, or preferred action rather than a neutral fact.

Examples:

• Es mejor que salgas ahora.
• Es mejor que lo hagas mañana.
• Es mejor que no conduzcas cansado.

So your sentence follows a very common pattern:

• Es mejor que + subjunctive

Yes, you could, but it is a little different.

• girar a la izquierda = the standard, simple way to say turn left
• girar hacia la izquierda = turn towards the left

In driving contexts, girar a la izquierda is usually the most natural and common phrasing.

So in this sentence, a la izquierda is the best choice.

Because the speaker is phrasing the idea as advice rather than as a direct command.

Compare:

• Pon el intermitente antes de girar a la izquierda.
  = direct command: Use your indicator before turning left.
• Es mejor que pongas el intermitente antes de girar a la izquierda.
  = softer advice: It’s better if you use your indicator before turning left.

So the sentence is less forceful and more polite or explanatory than a straight imperative.

Yes. Spanish allows some flexibility, although the original order is the most neutral.

You could also hear:

• Es mejor que pongas el intermitente antes de girar.
• Antes de girar a la izquierda, es mejor que pongas el intermitente.

Both are grammatical. The second one puts more focus on the time sequence: before turning left.

The original version is very natural and straightforward.