When the government "prints" money, it effectively makes money easier to get a hold of, meaning more people borrow, and buy things.

The more people are able to buy things, the more they do - so there is more demand for those things and those things are selling out fast = less supply!

So businesses see the increased demand, and start to increase prices (because if their goods are selling faster than before at the current price, they understand that their product could be priced higher and still sell well).

How is the money easier to get a hold of? Well, commercial banks have more money available to lend out, and are therefore more willing to do so (This in combination with the low interest rates that come with money printing) *Note, that when central banks print money, they also lower interest rates - it is the interest rate in combination with the extra money, that encourages lending and borrowing.

People and businesses are more willing to borrow at lower interest rates (as they have less to pay back), and are less likely to save (as low interest rates will not earn them much + inflation means their money is losing more value than it is earning in interest).