Learn Swedish: Flaskan skakas innan mjölken värms. - The bottle is shaken before the milk is heated.

It creates the passive voice, which focuses on the action happening to the object rather than who is doing it. In English, we say "is shaken" and "is heated." In Swedish, you form this by adding an -s to the verb. This is very common in recipes, rules, and instructions where it doesn't matter who is actually doing the shaking or heating.

How exactly do I form this passive -s ending in the present tense?

For most verbs that end in -ar in the present tense, like skakar (shake), you drop the -r and add -s to get skakas. For verbs that end in -er, like värmer (heat), you drop the -er ending entirely and add -s to the base word, giving you värms.

Why use innan for "before" here instead of före?

Innan is used because it is followed by a full mini-sentence that has its own verb (mjölken värms). You use före when it is followed only by a noun or pronoun, like in före frukosten (before breakfast).

Could I write this as a direct instruction, like "Shake the bottle"?