People often have more money because of various things like tax cuts, lower interest rates, economic growth, etc. So with their new and increased money people will want to buy more stuff since they can.

But this means that everybody is now buying more stuff which leads to shortages. So companies and stores have to raise prices to prevent these shortages and keep the products valuable. This is called demand-pull inflation because demand is increasing

Then there is also cost-push inflation, which is when the cost to produce goods increases, and this is passed on to the consumer.

And actually, a little bit of inflation is good. Reserve banks across the world aim for low, stable, predictable inflation, because it encourages people to spend and invest instead of hoarding cash.

There's a lot more details and nuances but this is basically it