Learn Dutch: Oké, ik kom morgen. - Okay, I am coming tomorrow.

Dutch doesn't use an "-ing" form for verbs like English does. To say "I am coming", you just use the simple present tense: ik kom (which literally means "I come").

Doesn't morgen also mean "morning"? How do I tell which meaning is used here?

Yes, morgen means both "tomorrow" and "morning". You have to use context to tell them apart. "I am coming morning" doesn't make sense, so it must mean "tomorrow". If you specifically want to say "tomorrow morning", the word is morgenochtend.

Why is there an accent mark on the e in Oké?

The accent shows that you should pronounce it as a long vowel, like the "ay" in the English word "okay". Without the accent, an e at the end of a Dutch word is usually pronounced as a soft "uh" sound.

Could I put the word morgen at the beginning of the sentence?

Yes, you can! You could say Oké, morgen kom ik. Notice that when you start the sentence with a time word like morgen, the subject (ik) and the verb (kom) swap places.