Die Ersatzlieferung kommt am Freitag.

Because Ersatzlieferung is a feminine noun.

A very useful rule for German compounds is this: the last part decides the gender. Here, the last part is Lieferung, and die Lieferung is feminine. So the whole compound is also feminine:

• die Lieferung = the delivery
• die Ersatzlieferung = the replacement delivery / replacement shipment

So the article has to be die.

It is a compound noun:

• Ersatz = replacement / substitute
• Lieferung = delivery / shipment

Together, Ersatzlieferung means a delivery that replaces something defective, missing, or incorrect.

German uses compound nouns very often, where English might use several separate words.

Because the subject is singular: die Ersatzlieferung.

So the verb must match it:

• Die Ersatzlieferung kommt = singular
• Die Ersatzlieferungen kommen = plural

Here, there is only one replacement delivery, so German uses kommt.

This is very normal in German. The present tense is often used for the future when the time is already clear.

Here, am Freitag makes the future meaning obvious, so kommt is enough:

• Die Ersatzlieferung kommt am Freitag.

German does this much more often than English. English often prefers is coming on Friday or will arrive on Friday, but German is perfectly happy with simple present in this kind of sentence.

am is a contraction of an dem.

For days of the week, German usually says:

• am Montag
• am Dienstag
• am Freitag

This corresponds to English on Monday / on Tuesday / on Friday.

So:

• an dem Freitag → am Freitag

The contracted form am is the normal one.

It is in the dative, because an in this time expression takes the dative.

You can see that in am, which comes from an dem. The dem is dative.

So even though Freitag itself does not change form, the structure shows dative:

• an dem Freitag → am Freitag

Also, Freitag is masculine as a noun: der Freitag.

Because German main clauses normally follow the verb-second rule.

In this sentence:

• Die Ersatzlieferung = first position
• kommt = second position
• am Freitag = the rest

So the pattern is:

• Die Ersatzlieferung | kommt | am Freitag.

This is one of the most important word-order rules in German.

Yes, absolutely.

That version is also correct, and it follows the same verb-second rule:

• Am Freitag = first position
• kommt = second position
• die Ersatzlieferung = after the verb

The meaning is basically the same, but the emphasis changes a little:

• Die Ersatzlieferung kommt am Freitag.
  Slightly more neutral.
• Am Freitag kommt die Ersatzlieferung.
  Puts more focus on Friday.

Yes. It is very natural in everyday German.

German often uses kommen for things like packages, orders, or deliveries arriving:

• Das Paket kommt morgen.
• Die Bestellung kommt nächste Woche.
• Die Ersatzlieferung kommt am Freitag.

Depending on context, you might also hear more formal alternatives such as:

• Die Ersatzlieferung wird am Freitag geliefert.
• Die Ersatzlieferung trifft am Freitag ein.

But kommt is simple, common, and idiomatic.

Because they are both nouns, and all nouns are capitalized in German.

• Ersatzlieferung = noun
• Freitag = noun

Days of the week are nouns in German, so they are capitalized too:

• Montag
• Dienstag
• Freitag