Daarom koopt Sofie kaas in de supermarkt en stopt die in haar boodschappentas.

Because Dutch main clauses usually follow the verb-second (V2) rule.

That means:

• the finite verb must come in the second position
• whatever comes first can be the subject, but it can also be an adverb like daarom

So:

• Sofie koopt kaas... = subject first
• Daarom koopt Sofie kaas... = adverb first, so the verb still stays second, and the subject moves after it

This kind of subject-verb inversion is very common in Dutch.

Yes, that is also grammatical.

The difference is mainly focus:

• Daarom koopt Sofie kaas... puts emphasis on therefore / for that reason
• Sofie koopt daarom kaas... starts with Sofie, so it feels more neutral or more focused on her

Both are correct Dutch main-clause word orders.

Because Dutch, like English, often leaves out the subject in the second clause when:

• the clauses are joined by en
• the subject is the same

So this is understood as:

• Daarom koopt Sofie kaas in de supermarkt en (Sofie) stopt die in haar boodschappentas.

Repeating Sofie would still be possible, but it would sound less natural unless you want extra emphasis.

Because en is joining two main clauses here:

1. Daarom koopt Sofie kaas in de supermarkt
2. (Sofie) stopt die in haar boodschappentas

Each clause needs its own finite verb:

• koopt
• stopt

So en stopt means and puts.

It is not like English to buy and put after another verb. These are two separate present-tense actions in a coordinated sentence.

Because die is a common pronoun for a previously mentioned de-word thing.

• de kaas → die
• het brood → usually dat

So:

• Sofie koopt kaas en stopt die in haar boodschappentas.
• Sofie koopt brood en stopt dat in haar boodschappentas.

Dutch often uses die/dat to refer back to objects, especially things, where English would usually just say it.

Because kaas is being used as an uncountable/mass noun here, like English cheese.

So:

• Sofie koopt kaas = Sofie buys cheese

If you wanted to talk about a specific cheese or a whole cheese, you might use an article or a more specific noun phrase, for example:

• een kaas
• de kaas
• een stuk kaas

But in this sentence, kaas just means cheese in general.

Dutch often uses in both for:

• being inside something
• moving into something

English often distinguishes:

• in = location
• into = movement

Dutch usually does not make that distinction in the same way.

So:

• in de supermarkt = in the supermarket
• stopt die in haar boodschappentas = puts it in / into her shopping bag

The meaning comes from the verb and the context.

No. Here stoppen means to put or to stuff/place something into something.

So:

• stopt die in haar boodschappentas = puts it into her shopping bag

This is a very common use of stoppen in Dutch. It does not mean ceases here.

Because haar means her, and it shows whose bag it is.

So:

• de boodschappentas = the shopping bag
• haar boodschappentas = her shopping bag

Dutch possessives work much like English ones:

• mijn = my
• jouw/je = your
• zijn = his
• haar = her
• ons/onze = our

Because Dutch usually writes compound nouns as one word.

Here:

• boodschappen = groceries / shopping
• tas = bag

Together:

• boodschappentas = shopping bag

This is very normal in Dutch. English often separates these words, but Dutch usually combines them.

Because they are present tense, third person singular forms.

The infinitives are:

• kopen = to buy
• stoppen = to put / place / stuff

With Sofie (she), the present tense is:

• ik koop
• jij koopt
• Sofie koopt

and:

• ik stop
• jij stopt
• Sofie stopt

So the -t ending is the normal present-tense form for he/she/it and usually jij/je.

Related, yes. Die can be:

• a demonstrative determiner: die supermarkt = that supermarket
• a demonstrative pronoun: Ik koop kaas en stop die in mijn tas = I buy cheese and put that / it in my bag

In this sentence, die is a pronoun replacing kaas.

So it is not directly translating word-for-word as English that in the most natural way; in context it functions more like English it.