In basic terms, you take out a mortgage from a mortgage lender as a long term loan to make payments on a property.
The mortgage lender has the option of taking possession of the property and selling it on if the mortgage repayments aren’t made. This is so that the lender doesn’t lose money as they would be making it back from the property sale.
Any time you take out a mortgage, the loan is then split into two aspects. One of which is the interest , which is what the lender charges for lending the money. The other is the capital, which is the actual amount of money used to purchase the property.