Watch and read as much of the material that Tiller has prepared about how to you use the sheets as you can.
Only modify the cells that you are supposed to modify in the sheets. I use Google Sheets, but I believe it’s the same in Excel: as a general protocol, the cells you can safely modify have a light green background color (other than on the transactions sheet). It seems like a lot of folks get themselves in trouble by modifying other cells that have complicated and critical formulas in them. Whether intentionally or inadvertently, they modify those cells and break their sheets by doing so.
You can always revert back to a previous version, so it’s hard to do any damage that is unfixable.
The Tiller Foundations Guide is a good starting point. Just go at your own pace and discover what works for you.
Some people use the default Foundation Template and keep it simple.
Some people experiment and try all the various solutions that are available.
Your data is in spreadsheets, so the options are endless.