The lender's rights are stated in the mortgage document. Usually, you have various obligations, such as keeping the premises insured and in good condition.
You are also prevented from some actions - such as leasing the premises to someone else - without the lender's permission. If you plan to let the premises, it is a good idea to check from the outset that this will be allowed.
Of course, you are also required to pay interest and make repayments of the mortgage as agreed. If you fail to make payments, or otherwise breach the terms of the agreement, the lender can appoint a receiver to take control of the premises. They can then sell the premises (and use the proceeds towards paying off your debt).
