A mortgage is a loan to buy a home — secured against that home. The bank lends you most of the purchase price, and you pay it back over 25–35 years with interest.
The part you contribute upfront is your deposit. Lenders typically want at least 5% of the property's value. For a £220,000 home, that's about £11,000.
The bigger your deposit, the less you borrow — and lenders offer better rates when you're borrowing less. A 10% deposit will nearly always get you a better deal than 5%.
Lenders work out how much they'll offer based on your income — usually 4 to 4.5 times your annual salary. Add your deposit to that, and you have your total budget.