If your rent income is less or not much more than the mortgage payment you don't necessarily have a loss. In fact you may end up showing a net profit on your tax return.
If you don't understand the accounting you should sit down with an accountant to explain it to you.
Here's some tax guides and videos on Rentals
https://turbotax.intuit.com/tax-tips/rental-property/
What kind of Rental expenses can I deduct?
https://ttlc.intuit.com/community/credits-and-deductions/help/what-kinds-of-rental-property-expenses-can-i-deduct/00/26372
What is Depreciation?
https://ttlc.intuit.com/community/rental/help/what-is-rental-depreciation-and-how-does-it-differ-from-an-expense/00/26371
IRS publication 527 on Rental Property….
http://www.irs.gov/pub/irs-pdf/p527.pdf