Learn Dutch: Ze koopt morgen bloemen in de supermarkt. - She is buying flowers at the supermarket tomorrow.

In English, we usually put the time ('tomorrow') at the very end of the sentence. In Dutch, time expressions like morgen usually want to be early in the sentence, right after the verb. A major rule in Dutch is 'Time before Place', which is exactly why morgen comes long before in de supermarkt.

Why does the object bloemen come after morgen instead of right after the verb?

In English, we like to keep the verb and the object together ('buying flowers'). In Dutch, the time expression (morgen) jumps in between the verb and a non-specific object like bloemen (flowers in general, not 'the' flowers). So the typical Dutch pattern here is Verb -> Time -> Object -> Place.

The translation says 'is buying... tomorrow', but isn't koopt just the present tense?

Yes, koopt is the present tense ('buys' or 'is buying'). In Dutch, you can easily use the present tense to talk about future plans, as long as you include a future time word like morgen so the meaning is clear.

Why do we use in for 'at the supermarket'?

Prepositions rarely translate perfectly between languages! In Dutch, you focus on the fact that you are inside the building when shopping, so you use in de supermarkt. If you used bij de supermarkt, it would sound like you are buying them at a stand outside, near the building.