Pre-Trump, the average global tariff rate was 2.5%. The US and the EU were among those with average rates in the 2% range. The countries with the highest tariffs (in the high teens or around 20%) tend to be very small and/or very poor.
They are generally used sparingly, to protect vulnerable but industries that are of high importance to their nations economy.
Trump's tariffs are enormous, and apply to (almost) all goods. The baseline rate of 10% is, itself, 4 times the global average, and many countries have been hit with far higher ones.
He had said they were going to be reciprocal ("we'll tariff you what you tariff us") but they are not, they go magnitudes higher, because his (stupid) math factors in the country's trade deficit.
Trump, it seems, feels like a country is "ripping off" the US if the US buys more from them than they do from it. For example, he has hit Lesotho (a small African country, with a population of less than Wales') with the highest rate of tariffs. The US buys tens of millions of dollars of diamonds from Lesotho each year, as well as a lot of clothing.
Trump thinks that, somehow, the ~2.5m people of Lesotho, more than half of whom live below the poverty line, should be spending the same on US goods as the ~350m people in the US spend on goods from Lesotho. If the average person from Lesotho was 100 times richer than the average American, that would be a slightly more reasonable (if still absurd) ask.
The US accounts for around half of Lesotho's exports, so their economy will be decimated.
Which, apparently, is intended to make them spend more on US products?
It's hard to tell if it's more stupid or evil.
And, of course, China has, and other countries will, retaliate.
Either way, the US is picking a trade war it can't possibly win. I think the biggest question is if Trump really believes (contrary to all sense) that it'd be good for the US in the long term, or whether he's deliberately crushing the economy, people and businesses in order to consolidate his power over them.
The tariffs are bad for the whole world but are economic suicide for the US. I just worry that he'll do something else crazy, like invade Greenland, to distract from it.