Jeg lægger bagepapir på bagepladen, før jeg sætter bollerne i ovnen.

Danish often uses different placement verbs where English just uses put.

• lægge is used when something is laid down, especially something flat:
  lægger bagepapir på bagepladen = putting baking paper down on the tray.
• sætte is often used when something is placed somewhere in a more general or upright/set position, and sætte i ovnen is very natural for putting something into the oven.

So the choice depends on how the object is being placed, not just the general idea of putting.

Because bagepapir is being used like a material/substance noun, similar to paper, water, or bread in English.

Here it means some baking paper, not a baking paper. Danish often leaves out the article with this kind of noun when speaking generally:

• Jeg køber mælk = I buy milk
• Jeg bruger smør = I use butter
• Jeg lægger bagepapir på bagepladen = I put baking paper on the tray

If you wanted to refer to a specific sheet, you might say et stykke bagepapir or sometimes bagepapiret, depending on context.

Those endings show the definite form in Danish.

• bageplade = a baking tray
• bagepladen = the baking tray
• bolle = a roll/bun
• bollerne = the rolls/buns
• ovn = an oven
• ovnen = the oven

Unlike English, Danish usually adds the definite article to the end of the noun instead of using a separate word like the.

Because the prepositions match the physical relationship:

• på = on a surface
  på bagepladen = on the baking tray
• i = in an enclosed space
  i ovnen = in the oven

So Danish works very much like English here: the paper goes on the tray, and the buns go in the oven.

Because før introduces a subordinate clause, and subordinate clauses in Danish do not use normal main-clause inversion.

In a main clause, Danish usually has verb-second word order:

• Jeg sætter bollerne i ovnen
• Nu sætter jeg bollerne i ovnen

But after før, the clause is subordinate, so the word order is more straightforward:

• før jeg sætter bollerne i ovnen

That is why jeg comes before sætter.

Because Danish often uses the present tense for:

• everyday routines
• instructions
• describing what someone is doing step by step

So Jeg lægger ... før jeg sætter ... can sound like:

• This is what I do
• I’m doing this now
• This is the usual procedure

English often uses the present progressive in similar contexts, but Danish normally just uses the simple present.

Because the second part is its own clause and needs its own subject.

The sentence has two clauses:

• Jeg lægger bagepapir på bagepladen
• før jeg sætter bollerne i ovnen

Even though the subject is the same person, Danish still says jeg again. English does the same:

• I put baking paper on the tray before I put the buns in the oven.

Yes. Danish makes very frequent use of compound nouns.

• bage = baking / bake-related
• papir = paper
  → bagepapir = baking paper
• plade = tray/plate/sheet
  → bageplade = baking tray

This is extremely common in Danish, and native English speakers often need to get used to the fact that these compounds are usually written as one word.

Yes. You could say:

Før jeg sætter bollerne i ovnen, lægger jeg bagepapir på bagepladen.

When the før-clause comes first, the main clause must follow normal Danish verb-second order, so you get:

• lægger jeg not
• jeg lægger

That inversion is one of the most important word-order patterns in Danish.

Danish often uses the definite form when the object is specific from the situation, even if English might be a bit more flexible.

In a kitchen context, the baking tray and the oven are understood as the relevant ones, so:

• på bagepladen
• i ovnen

sound very natural. Danish often prefers the definite form when both speaker and listener can easily identify the thing being talked about.