How do I properly split my savings between a bank account and investments?

The main thing is to first set aside an emergency fund covering 3-6 months of living expenses - that should be in an easily accessible account. After that, you can split the rest between savings and investments depending on when you'll need the money: keep in your account what you might need in the next few years, and invest what you can leave untouched for 5-10 years. A lot of people recommend rules like 70/30 or 80/20, but it really depends on your age, income, and goals, so go by your own plans rather than someone else's ratios.

You should keep an emergency fund in your account, and the rest you can invest - but only if you're ready for the fact that investments don't always go up and sometimes drop. Everyone has a different risk tolerance, so there's no one-size-fits-all formula.