Hi Hazan. "To be off to" is to be going somewhere, and we often use it announce that we're leaving. For example: "I'm off to work. Have a nice day." "It's 8:50 AM! I should be off to school!" I'm off! See you later (you can see this as you're leaving work, school, or a party, etc). Hope that helps. Let me know if you have questions :-)

"To be off to" means to leave for somewhere or to go somewhere. "I am off to" is the idiom. Example: I am off to the market. I am off to America next Monday.