I’m a scientist, not an economist

I'm neither lmao. We just had a macroecon credit in my degree program, which is where I learnt about this.

Halp!

Now onto this... You're kinda right but kinda wrong in that fractional reserve banking "creates money". Here's a way to think about putting your money in a bank. By opening a bank account, you are not putting your money in a vault. You are loaning it to the bank. The bank then loans it out to another person, who then "loans" it to another bank. Hence, fractional reserve banking is a natural side effect of this logic. What would happen if we had a 100% fractional reserve? Well, the bank wouldn't be able to loan your money to anyone then. It would essentially become a vault.

Therefore, fractional reserve banking is necessary to make loaning money possible. Loaning money is necessary for obvious reasons.

Now to the "creating money" part. Sure, at the macro scale, you get a lot of virtual money in the economy. At the micro level though, individual banks aren't creating money. They still have to get the money that they've lent out back. If they fail to do so, they're going to go bankrupt. Banks would never go bankrupt if they could print money on a micro scale, right?

Okay, so now let's zoom out back at the macro scale. Now, you can accelerate or decelerate the economy by controlling the ratio of money that is in circulation vs money that is out of circulation. It's simple- more money in economy = more demand = more profits = more investments in increasing supply to be competitive = more work done. If this demand however drops, profits drop, and increase in supply drops. This is very bad as no work will be done. However, if demand increases too much for essential goods (like food, housing, etc.), it is bad as it can cause problems for people till the supply can catch up. The economy is going too fast in such cases.

Now, you can slow the economy down by many ways- by increasing interest rates, increases the fractional reserve and so on. This way, less people are going to borrow (you just reduced demand by this simple technique). You now reduced demand in your economy and slowed it down. The opposite can be done to speed the economy up.