Learn French: Ils vont aux États-Unis demain. - They are going to the United States tomorrow.

États-Unis (United States) is a plural country name. In French, when you are going to or are located in a country with a plural name, you always use aux. For feminine countries you use en (like en France) and for masculine countries you use au (like au Japon).

How do you pronounce aux États-Unis? Are there silent letters?

There are actually two required liaisons (linking sounds) here! The letter x at the end of aux links with the vowel É to make a z sound. Then, the s at the end of États links with the U in Unis to make another z sound. Altogether, it flows together smoothly like "oze-ay-tah-zew-nee".

I vaguely remember the verb for "to go". What is the dictionary form of vont?

The infinitive (dictionary form) is aller. It is a very irregular verb. Vont is the form for ils (they, masculine) or elles (they, feminine). Because it is used so often, you just have to memorize forms like je vais (I go) and ils vont (they go).

Can I put demain at the beginning of the sentence instead?