Learn German: Jeder Star hat halt Geheimnisse. - Every star simply has secrets.

halt is a modal particle used to express that something is just a fact of life. It translates best to "simply" or "just." It gives the sentence a conversational tone of acceptance, as if saying, "Well, every celebrity has secrets, and that is just the way it is."

Why is it Jeder with an -er ending here?

jeder means "every" and it changes its ending based on the gender and case of the noun it describes. Because the word for celebrity, der Star, is masculine and acts as the subject of the sentence (nominative case), jeder takes the masculine nominative ending -er.

Does Star mean a star in the night sky, too?

No, German borrowed the English word Star specifically to talk about famous people or celebrities. If you want to talk about a literal star in the sky, you would use the German word der Stern.

Why does the plural word Geheimnisse have a double "s" when the singular is Geheimnis?

The singular word is das Geheimnis (the secret). As a rule in German, nouns ending in -nis double their s when you add an ending to make them plural, which is why it becomes die Geheimnisse.