A credit score is a number lenders use to estimate the risk that you will not repay borrowed money. It is calculated from your borrowing history, not from your income or savings.
The heaviest factors are almost always payment history and how much of your available credit you are currently using. Length of history, the mix of credit types and recent applications matter less. Utilisation can shift within a billing cycle or two, which makes it the fastest lever; missed payments fade far more slowly. Exact weightings and score ranges differ by country and by scoring model.