אם יהיה משלוח מחר, אני אאסוף את החבילה בדרך הביתה.

Because this sentence is talking about a future condition.

In English, we usually say If there is a delivery tomorrow, I'll pick up the package, using present tense after if.
In Hebrew, for a real future condition, it is normal to use the future tense in both parts:

• אם יהיה משלוח מחר = if there will be a delivery tomorrow
• אני אאסוף את החבילה = I will pick up the package

So this is standard Hebrew grammar, even though English works differently.

יהיה is the masculine singular future form of להיות (to be).

Here it does not mean just will be in the simple copula sense. It is being used in an existential sense:

• יש משלוח = there is a delivery
• יהיה משלוח = there will be a delivery

Since משלוח is a masculine singular noun, Hebrew uses יהיה.

Because משלוח is grammatically masculine.

Hebrew verbs in the future often agree with the noun they refer to, especially in sentences like there will be... So:

• יהיה משלוח = there will be a delivery
• תהיה חבילה = there will be a package

Even though חבילה is feminine, the word in this clause is משלוח, so יהיה is correct.

They are related, but not the same.

• משלוח = delivery / shipment
• חבילה = package / parcel

So in this sentence:

• אם יהיה משלוח מחר = if there is a delivery tomorrow
• אני אאסוף את החבילה = I’ll pick up the package

A delivery may contain a package, but the words are not interchangeable in every context.

Because two different things are happening at once:

1. The first א is the future-tense prefix for אני (I).
2. The verb root itself begins with א: אסף (to collect / gather / pick up).

So:

• root: אסף
• future, I: א + אסוף
• result: אאסוף

This is completely normal in Hebrew spelling. It may look strange at first, but it is not a typo.

Here, את is the direct object marker, not the word with.

In Hebrew, את is placed before a definite direct object. It usually has no separate translation in English.

So:

• אני אאסוף את החבילה = I will pick up the package

The את is there because החבילה means the package, which is definite.

Important: Hebrew also has forms related to with, like איתי (with me), but that is not what is happening here.

The ה is the Hebrew definite article, meaning the.

• חבילה = a package
• החבילה = the package

So את החבילה means the package, not just a package.

Literally, it is something like on the way homeward.

Breakdown:

• בדרך = on the way
• הביתה = home / homeward

Together:

• בדרך הביתה = on the way home

This is a very common Hebrew expression.

הביתה is a special and very common form meaning homeward / to home.

The final ־ה is an old directional ending that can mean movement toward a place. So:

• בית = house / home
• הביתה = homeward / to home

In modern Hebrew, הביתה is the normal way to say home when someone is going there:

• אני הולך הביתה = I’m going home

So בדרך הביתה is the natural phrase for on the way home.

Because ב־ (in / on / at) is a prefix in Hebrew and attaches directly to the following word.

So:

• ב + דרך = בדרך

Also, when a definite noun is involved, Hebrew often combines the preposition and the article in writing. In a phrase like בדרך הביתה, the overall meaning is simply on the way home.

Yes. Hebrew word order is somewhat flexible.

For example, you could also say:

• אני אאסוף את החבילה בדרך הביתה אם יהיה משלוח מחר.

That still means the same thing.
The original order puts the condition first, which sounds very natural:

• אם יהיה משלוח מחר, ... = If there’s a delivery tomorrow, ...

So the version you were given is a normal, standard way to say it.

Usually, אם יהיה משלוח מחר is better here because the sentence refers to the future.

• יש = there is / there are (present)
• יהיה = there will be (future)

Since tomorrow is future, Hebrew normally prefers יהיה:

• אם יהיה משלוח מחר = if there is / will be a delivery tomorrow

You may sometimes hear present forms used in very conversational speech, but the standard and most natural form here is יהיה.