How do morgages work ?

Say you wanted to buy a flat and you're like 18 (which I'm not but I'm using it as a example) and you've only got like a job which doesn't pay too badly but you don't have enough for your flat and your buying it alone how does like a morgage work how...

could arrange one, and how do I pay it back ?

I am just curious but I was thinking about the future and it started to stress me out

I'm not sure how they work over there, but here, you have to go through the bank to get the mortgage, which pays off the house and you pay the bank in return with interest.

Buy a flat? What are you talking about???

I know where I'm from, most company's will not give a mortgage to an 18 year old, unless you have a parent or older person as a co-signer. It's too much of a risk for the company to take them.

You can call your local banks and talk to them about loans and find out what you can qualify for and how much.

You need to make sure that the bank will make money off the land if you dont pay. Look at it this way:
Option 1:
House appraised at 180,000 dollars, it is for sale at 190,000 dollars. You go to the bank and tell them that you want that house. Bank says not without a down payment because we might lose money if we foreclose.
Option 2:
House appraised at 190,000 dollars but the seller is very motivated and wants to sell it for 180,000 dollars. The bank will probably through there money behind this because if you dont pay them and they have to take it back, then it would be easy to sell because its below market value.