hikkosigyousya ga kuru mae ni, danbooru wo genkan ni oite okimasu.

Here, 引っ越し業者が来る means the movers come / the moving company comes.

が marks 引っ越し業者 as the subject of 来る. This is especially natural inside a time clause like 来る前に (before they come).

If you used は, it would sound more like you were making the movers the topic, often with a contrastive nuance. In this sentence, が is the most neutral and natural choice.

With 前に (before), Japanese normally uses the dictionary/plain non-past form of the verb:

• 来る前に = before someone comes
• 食べる前に = before eating

This is because the action in that clause has not happened yet at the time of the main action.

A useful comparison:

• 来る前に = before coming
• 来た後で = after coming

So 前に often goes with the plain non-past form, while 後で / あとで often goes with the past form when the action is completed first.

前に means before.

The structure is:

[short clause] + 前に

So:

引っ越し業者が来る前に
= before the movers come

The whole first part acts like a time expression for the main action:

段ボールを玄関に置いておきます
= I’ll put the cardboard boxes in the entryway in advance

They do two different jobs:

1. 前に
   This に is part of the time expression before.

2. 玄関に
   This に marks the place where something is put.

So:

• 来る前に = before coming
• 玄関に置く = put something in/at the entrance

Even though the particle is the same, the function is different in each part.

Because 置く is a verb of placement, and Japanese usually marks the place where something ends up with に.

• 机に本を置く = put a book on the desk
• 玄関に段ボールを置く = put the boxes in/at the entrance

で marks the place where an action happens in general, but with 置く, the important idea is the resulting location, so に is the normal choice.

置いておきます is 置く plus 〜ておく.

〜ておく often means:

• do something in advance
• do something and leave it that way for later convenience

So:

• 置きます = I will put/place it
• 置いておきます = I will put/place it in advance (and leave it there ready)

In this sentence, that nuance is important: the boxes are being placed by the entrance before the movers arrive, so they’re ready.

Japanese nouns usually do not show singular vs. plural the way English nouns do.

So 段ボール can mean:

• a cardboard box
• cardboard boxes
• cardboard

In this sentence, because of the moving context, it most naturally means cardboard boxes.

The exact number is understood from context, not from the noun form itself.

引っ越し業者 means moving company or movers.

It is made of:

• 引っ越し = moving house / moving
• 業者 = company, operator, contractor, service provider

So the phrase refers to the people or company handling the move.

Depending on context, English may translate it as:

• the moving company
• the movers

In Japanese, the non-past form covers both:

• present
• future

So 置いておきます can mean:

• I put it in advance
• I will put it in advance

Here, because of the context (before the movers come), it is understood as a future plan.

This is very normal in Japanese.

Not exactly.

玄関 refers to the entryway / entrance area of a home, especially the Japanese-style space just inside the door where people remove their shoes.

So 玄関に置いておきます does not necessarily mean right at the front door. It means something more like:

• put it in the entryway
• leave it by the entrance

Japanese usually puts the verb at the end, and other parts come before it.

This sentence is roughly structured like this:

• 引っ越し業者が来る前に = before the movers come
• 段ボールを = the cardboard boxes
• 玄関に = in the entryway
• 置いておきます = will place in advance

So Japanese builds up the information first and gives the main verb last. That is one of the biggest differences from English word order.