Learn German: Wir treffen dich morgen. - We are meeting you tomorrow.

dich is the accusative (direct object) form of du (you). Since "you" are the one being met, "you" are receiving the action of the verb treffen, so we use the accusative case.

The English translation says "are meeting", but isn't treffen in the present tense?

Yes! In German, you can often use the present tense to talk about the future, as long as there is a time word that shows when it's happening. Here, the word morgen (tomorrow) makes it clear that this is a future event.

Could we put morgen at the beginning of the sentence?

Yes, you can say Morgen treffen wir dich. Notice that the verb treffen must always stay in the second position, so the subject wir moves to the third spot, right after the verb.

Wait, doesn't morgen mean "morning"?

It depends on the capitalization! Written with a lowercase m, morgen is a time word meaning "tomorrow". Written with a capital M, der Morgen is a noun meaning "the morning".