So i wrote a composition in french and my teacher marked that i conjugated a verb incorrectly. I can't figure out what it is supposed to be (i don't know if i'm using an incorrect idiom, etc). The original sentence is,

"Quand vous allez a l'interieur, la premiere..." he says that 'allez' is wrong, but i don't know why.

4 answers

The conjugation is correct if the present indicative tense was requested, but it seems to require a different tense.

Please post the context, namely the environment surrounding the sentence, was it in the past, was it a hypothetical situation, was it an instruction to someone, etc.

The best is to post the whole paragraph or even the whole text. This will give Mme Sra the whole picture to help you.
Definitely we need to see the instructions of what you were to do. Possibly you were studying the use of the Future with quand, lorque, aussitôt que, dès que, après que, where "if the action refers to the future" French uses the future or less frequently the future perfect.

Some examples:

Donnez-lui mes amitié lorsque vous la verrz. = Give her my regards when y ou see her.

Aussitôt qu'ils arriveront, nous partirons. = As soon as they arrive, we shall leave.

Le ferez-vous apré que nous reviendrons (serons revenus)? = Will you do it after we return ?

In other cases, the tense uswed after these con junctions is similar to the English = present, passé composé, etc.

I suspect then that your sentence would begin with: Quand vous irez, etc.

Sra (aka Mme)
I am thinking it should have been "irez" instead of "allez".

which would be future progressive.
"Le ferez-vous après", pas "apré" ><"