Learn German: Wenn du dein Sternzeichen kennst, wirst du alles verstehen. - If you know your zodiac sign, you will understand everything.

This sentence uses the future tense (Futur I). You form this by combining the helping verb werden (here conjugated as wirst for "you will") with the infinitive of the main verb (verstehen). The conjugated helping verb takes the active verb spot, and the infinitive gets pushed to the very end of the clause.

Why does the second part of the sentence say wirst du instead of du wirst?

The first part of the sentence (Wenn du dein Sternzeichen kennst) is a subordinate clause. German treats this entire clause as occupying the first position of the main sentence. Because the main verb must always be in the second position, the verb wirst comes immediately after the comma. This forces the subject (du) to move after the verb, creating the classic "verb, comma, verb" pattern.

Why do we use kennst here for "know" instead of weißt?

German has two different verbs for "to know". You use kennen when you are familiar with a noun, such as a person, a place, or a thing like dein Sternzeichen (your zodiac sign). You use wissen when you know a fact, which is usually followed by a question word or a completely new clause.

Does wenn mean "if" or "when" here?

It can actually be both! In German, wenn is used for both conditions ("if") and time-related statements ("when" or "whenever" in the present or future). Based on the context of this sentence, "if" is the most natural English translation, but "when you know your zodiac sign" also makes perfect sense.