Learn German: Er wird das Zimmer buchen, obwohl das Wetter schlecht ist. - He will book the room although the weather is bad.

The word obwohl (although) is a subordinating conjunction. This means it introduces a dependent clause and forces the conjugated verb (ist) to jump to the very end of that clause.

Why is buchen at the end of the first part of the sentence?

The first part of the sentence uses the future tense. Just like with modal verbs, the helper verb (wird) takes the normal second position in the clause, and the main action verb in its dictionary form (buchen) gets pushed to the end of its clause.

Is the comma before obwohl strictly necessary?

Yes! In German, you must always use a comma to separate a main clause from a subordinate clause, such as the one starting with obwohl here.

Could I flip the sentence and start with obwohl?

Absolutely. You could say: Obwohl das Wetter schlecht ist, wird er das Zimmer buchen. Notice that because the entire obwohl clause acts as the first block of information, the verb of the main clause (wird) must come immediately after the comma to keep its strict second position.