You enter the total rent you actually received for the year. Then you enter your expenses like Mortgage Interest, Property Tax, Insurance, Repairs, etc. You can only deduct mortgage interest not the principal part of the mortgage. You should be depreciating the cost of the rental over 27.5 years, that will take care of the principal part of the mortgage.
If you don't see a spot for your expense on the Enter Common Expenses screen continue on and after about 3 screens of mortgage interest there is a screen asking Any Other Expenses.
Info on Rental Income and Expenses…….
https://ttlc.intuit.com/questions/1894483-where-do-i-enter-income-and-expenses-from-a-rental-propert... And FAQ on Schedule E
https://ttlc.intuit.com/questions/1901338-schedule-e-supplemental-income-and-loss Read pub 527 on Rental Property….
http://www.irs.gov/pub/irs-pdf/p527.pdf
