how can we know where to use will and where to use shall

please tell tommorow is my exam

when u r sure of some task accomplishment  there we use "will"  and when u r doubtedly saying to accomplish  anything without promising  there "shall"is used 

I SHALL  SUBMIT PROJECT TOMORROW !  HERE U HAVE DOUBT ON SUBMISSION

I WILL SUBMIT TOMORROW .  HERE U R SURE  IN SUBMISSION