Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of instructor],
Due to matters beyond my control, I'll be away from class from [departure date] to [returning date]. During this time I'll have limited access to phone and email.
Would you be able to provide me an outline of the material that will be covered during that time? I'll do my best to be up to date by the time I return.
Thank you for your assistance in this regard.