Most financial experts recommend having at least 3-6 months of expenses set aside as an emergency fund. This is used for true emergencies/things that you weren’t expecting (like a job loss or car accident). Hopefully these things never happen, but if they do, at least you’ll be covered. If you have to dip into your emergency fund, re-supply it as soon as you can to get it back to where it needs to be.
The “sinking fund” is something not as many people know or talk about. This is for known future expenses. For example, if you’re a 1099 self-employed individual, you better be setting aside money for taxes, because the tax man comes around every year to collect. And guess what? The car you drive? It will need an oil change and new tires every so often. Christmas and birthdays? They come at the same time every year, so if you plan on giving gifts, you should put money away in a sinking fund to cover those expenses.