Der Wind draußen ist stark, darum bleiben wir drinnen.

Wind is a masculine noun in German. As the subject of the sentence, it appears in the nominative case, which requires the definite article der for masculine nouns.
• Masculine nominative: der Wind
• Feminine nominative would be die, neuter das, plural die.

darum is a conjunctive adverb (also called a sentence adverb or linking adverb). It expresses “therefore” or “for that reason” and connects two main clauses. In German, when you join two independent clauses with a conjunctive adverb like darum, deshalb, or deswegen, you must separate them with a comma: Clause 1, darum Clause 2.

In German main clauses, the finite verb must occupy the second position. Since darum counts as the first element, the verb bleiben moves to the “second slot,” and the subject wir follows it: 1st position: darum
2nd position (finite verb): bleiben
then subject: wir.

Weil is a subordinating conjunction, not a conjunctive adverb. It introduces a subordinate clause that pushes the finite verb to the end. Example:
• With darum (main + main): “Der Wind draußen ist stark, darum bleiben wir drinnen.”
• With weil (main + subordinate): “Der Wind draußen ist stark, weil wir drinnen bleiben.”
Or more naturally: “Wir bleiben drinnen, weil der Wind draußen stark ist.” (Note how ist goes to the end in the weil‑clause.)

Yes. deshalb, deswegen, and darum are synonymous causal adverbs. They all mean “therefore”/“that’s why” and behave the same regarding comma placement and verb-second inversion: • “Der Wind draußen ist stark, deshalb bleiben wir drinnen.”
• “Der Wind draußen ist stark, deswegen bleiben wir drinnen.”

stark simply means “strong.” It’s the most common neutral adjective for any strong force (wind, rain, coffee, etc.). You can choose alternatives for nuance:
• heftig (violent, intense)
• kräftig (powerful)
• stürmisch (stormy)

• drinnen: a basic adverb meaning “inside” (in contrast to draußen).
• innen: also “inside,” but often used in more formal or attributive contexts (“an der Wand innen” – “on the inner side of the wall”).
• im Inneren: a noun phrase “in the interior,” often used in more abstract or descriptive contexts (“Im Inneren des Hauses ist es warm” – “Inside the house, it’s warm”).
In your sentence, the simple adverb drinnen is the most natural choice.