I'm not a money expert, or a financial advisor. The ideas I'm sharing are just a synthesis of things I've learned and try to stick to.
Budget is key. I don't use a lot of online apps, though they are available and some people love them. .
I use my credit union online banking service to keep track of my (non-cash) payments and my income. I pay all my regular monthly bills by direct pay. Before I did this, I'd always have a growing mountain of bills sitting on a side table, which I would avoid every day. The stress, plus the late fees, made my financial life a nightmare. Now I know they are paid on time, and I can track them easily.
To make my budget I started by making a list of every bill that comes in monthly or regularly. Insurance, taxes, utilities, cable and streaming services, garbage and snow removal, loans, etc. I added them up, decided which ones I could live without, and cancelled them. Add them up again and you have your monthly "nut." I subtracted the "nut" from my personal income. And voila, that's my spending money for the month.
BUT--- there are other regular expenses : the variables. Groceries, gas, dentist, appointments, vet bills.
If there are kids living at home, the variables can become intense. Mine no longer live at home, so that helps. College fees, though! That's a subject in itself. .