It isn't as easy as you think it is. First of all you have to buy the house and that means saving for a deposit payment you don't get all the money in a mortgage. Then you have to pay for certain repairs. If you are in the UK you also have to pay for the buildings insurance. By the time you have paid tax on the rent sometimes it is a lot less than the mortgage repayments.

You have to buy the house first, before you can rent it

The mortgage is not always less then the rental income,especially at the beginning.

You also need savings to cover any repairs, and any period when there is not tenant

As the saying goes, you must have money to make money. If you don't have the cash to buy rental properties, you're not going to buy them. Rent amounts must be set according to the local rental market - not according to "the mortgage."

Its ot hard, but you have to do your reserch. ALong with the mortgage, youhave insurance, taxes, repairs to pay. You have to pay these whether you have a tenant in there or not