As a pp says, start with a review. Print off six months of bank statements and work through them, accounting for every penny into different categories. If you tend to take out cash or you have lots of expenditures that you can’t account for, that’s your first lightbulb: your need to find a way of tracking and accounting for everything.
Once you’ve done this, you’ll have a fair idea of where all your money is going. So you can start to create a working budget. First, as up all your monthly income. Then, using the categories you’ve already come up with, list all your likely expenditures. Start with the essential ones that you can’t control - rent, council tax, any standing charges / direct debits for bills, insurance etc. Then ‘discretionary but necessary’ ones where you have some control over the amount, but can’t avoid - food, other groceries, toiletries. Then everything else.
you haven’t said if you are struggling or have plenty money but just don’t want to didn’t / waste as much. If you have surplus, decide what you want to do with it and ‘pay’ that first. Set up a savings account and a direct debit into it, which goes out straight after you’ve been paid. The goal could be a holiday, a deposit, pension, whatever: the trick is to ‘spend’ that money before it gets frittered away.
Tracking spending has to be active, done on a weekly basis ideally. Sit down with a bank state ment, and account for every penny that’s been spent. You need to commit to this. YNAB definitely makes this easier, but you still have to commit the time to it.