Learn French: Je fais réparer la voiture chez le garagiste. - I am having the car repaired at the mechanic's.

When you arrange for someone else to do a task for you, French uses the causative construction: a conjugated form of faire + an infinitive. Je fais réparer means 'I am having [it] repaired.' If you just said Je répare la voiture, it would mean you are holding the tools and fixing it yourself!

In English we put 'the car' in the middle ('have the car repaired'). Why is la voiture at the end here?

In the French causative structure (faire + infinitive), the two verbs must stick tightly together. You cannot separate them with a noun. Therefore, the object receiving the action (la voiture) always goes after the infinitive, never between fais and réparer.

Why do we use the preposition chez here instead of à (at)?

Chez means 'at the place or business of' and is used before a person or a profession. Because le garagiste refers to the mechanic (a person), we must use chez. If you wanted to refer to the physical building (le garage), you would use à and say au garage.

How do we know if this means 'I have the car repaired' (in general) or 'I am having the car repaired' (right now)?