You should listen to the chapo episode from 3/8 that just turned free. It's pretty much a lecture from Richard Wolff, a Marxist economics professor. He answers a lot of the questions you have in a great way

Central banks can create money out of thin air by way of loans. The interest rate on those loans is how expensive borrowing new money is. A high interest rate means that it's more expensive to borrow money so less of it gets created. A low rate means it's really cheap to borrow money, and sometimes crazy shit will happen like rates going to zero, which means money is free to borrow, or rates will go negative, which means the central bank is paying you to borrow money.

Central banks only loan out to other banks, and those banks are the ones businesses and people use, so any loan you'll ever get is going to be based on the prime interest rate the central bank set.

Inflation can be caused by a lot of things and isn't inherently bad. More people means you need more money. More economic growth means you need more money. But if there's more money and things haven't changed value, then each unit money is worth less, so prices go up.

In the last few years, inflation has mostly been driven the other way: companies increase prices because all the other companies increase prices as well, so everything costs more instead of being roughly equal in terms of value trade.

Monetary policy is really weird and it's basically a form of collective agreement magic.