If one didn't have such a spreadsheet and did't know how to start tracking such things as they were a bit financially illiterate, where would you recommend they start?
Export your last 6 - 12 months of transactions from your checking account, savings account, and/or credit card. Just getting the data is a good start.
Then you can bring those sheets together. What I did was combine my expenses across my debit card and credit card, then sort them into categories. Subscriptions, grocery (I shop at 2-4 stores regularly), hobbies, restaurants, etc.
I made a calculator in the sheet to convert my biweekly pay into monthly income. (there's slightly more than 2 pay periods per month, because a pay period is usually 28 days. I don't recall the exact number.) Once you have that, you can normalize all your expenses as well. For example, add up everything you spent on groceries in a 6 month period, divide it by 6. That's your mean monthly grocery bill.
It's a bit of work to get it all down but once you build the calculator it's not as much work to maintain it every month or six. I was able to figure out what it costs to maintain my lifestyle more or less, and then determine an amount I'm comfortable having automatically transferred to my savings account immediately after every paycheck comes through. (For me that also includes an amount that will go toward rent as I pay rent out of my savings account to ensure I never accidentally don't have money available.) Now I don't have to think about my savings often, I know it's going up at a certain rate. This also allowed me to take on some significant extra expenses to support my partner for a period of time without any fear.
