Am Donnerstag bringt die Post auch ein Paket, und ich kaufe frische Brötchen.

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

That means:

• position 1: one element comes first
• position 2: the finite verb comes next

In this sentence, Am Donnerstag is placed first, so the verb bringt must come immediately after it:

• Am Donnerstag | bringt | die Post auch ein Paket.

If the sentence started with the subject instead, it would be:

• Die Post bringt am Donnerstag auch ein Paket.

Both are grammatical, but the original version emphasizes Thursday first.

Am Donnerstag means on Thursday.

am is a contraction of:

• an dem

German often uses an with days of the week, and because Donnerstag is masculine (der Donnerstag), dem is the dative form.

So:

• an dem Donnerstag → am Donnerstag

This is very common:

• am Montag = on Monday
• am Freitag = on Friday

It can sometimes depend on context.

Most often:

• am Donnerstag = on Thursday / this Thursday / on Thursday in general context

If you want to clearly say on Thursdays as a repeated habit, German often uses:

• donnerstags

So:

• Am Donnerstag kaufe ich Brötchen. = On Thursday / this Thursday I buy bread rolls.
• Donnerstags kaufe ich Brötchen. = On Thursdays I buy bread rolls.

In real life, context usually makes the meaning clear.

Die Post usually means the mail, the postal service, or sometimes loosely the postman/postal delivery depending on context.

In this sentence, it most naturally means something like:

• the mail
• the postal service
• the post delivers

So Die Post bringt ein Paket means:

• The mail brings a package
• more natural English: The post delivers a package

German often uses die Post in this broader way.

A learner might wonder this because the forms themselves do not make it completely obvious:

• die Post could be nominative or accusative
• ein Paket could also be nominative or accusative

So how do we know?

Mostly from:

1. word order
2. meaning/context

In a normal German main clause with verb-second order, the noun phrase right after the verb is often understood as the subject if nothing else marks the case clearly.

So:

• Am Donnerstag bringt die Post auch ein Paket

is understood as:

• the mail = subject
• a package = object

Also, semantically, it makes much more sense that the mail brings a package than that a package brings the mail.

Here auch means also and it is closely connected to ein Paket.

So:

• die Post bringt auch ein Paket = the mail also brings a package

This suggests that a package is being added to something else already mentioned or understood.

For example, maybe the mail is bringing letters, and also a package.

Word placement matters with auch in German. It often appears near the thing it emphasizes. Here it most naturally emphasizes ein Paket.

Because after und, a new main clause begins, and that new clause follows normal main-clause word order.

So in:

• ..., und ich kaufe frische Brötchen.

the second clause has:

• ich = subject
• kaufe = finite verb

That is normal German word order for a main clause.

You only get inversion like kaufe ich when something else comes first in that clause, for example:

• ..., und am Donnerstag kaufe ich frische Brötchen.

So:

• und ich kaufe ... = correct
• und kaufe ich ... = not correct here

German often leaves out the article when talking about things in a general or indefinite way, especially plural nouns.

So:

• ich kaufe frische Brötchen = I buy fresh bread rolls

This sounds natural and means some fresh bread rolls, not a specific previously known set.

Compare:

• Ich kaufe frische Brötchen. = I’m buying fresh bread rolls.
• Ich kaufe die frischen Brötchen. = I’m buying the fresh bread rolls.
  (specific ones)
• Ich kaufe frische die Brötchen. = incorrect

Because the adjective ending depends on:

• case
• gender
• number
• whether there is an article before the noun

Here:

• Brötchen is plural
• it is the direct object, so it is accusative plural
• there is no article before it

With no article, the adjective takes the ending that shows the grammatical information. In the accusative plural, that ending is -e here:

• frische Brötchen

This is part of German adjective declension. Similar examples:

• Ich sehe große Hunde.
• Wir kaufen frische Äpfel.

Brötchen are small bread rolls, common in Germany.

A few useful things to know:

• singular: das Brötchen
• plural: die Brötchen

The singular and plural look the same in spelling, so the article or context tells you which is meant.

Also, -chen is a common diminutive ending in German. It often gives the noun a neuter gender:

• das Brot = bread
• das Brötchen = little bread / bread roll

So frische Brötchen means fresh bread rolls.

German often uses the present tense to talk about:

• present actions
• regular habits
• near future events

So this sentence could describe:

• something happening now as part of a routine
• something scheduled for Thursday
• a general plan

German does not need a special future form as often as English does. If the time is already clear from Am Donnerstag, the present tense is very natural.

This comma separates two full main clauses:

• Am Donnerstag bringt die Post auch ein Paket
• ich kaufe frische Brötchen

In German, a comma before und in this kind of sentence can be used to make the structure clearer, especially when the clauses are longer or have different subjects.

So the comma here helps show that these are two separate thoughts joined by und.