When you import something from another country, it needs to go through things like customs, etc. You have to fill out all the paperwork about what it is and where it’s going (if you’re using/selling it in the US or just middlemanning it somewhere else).

Part of that paperwork includes tariffs, a tax on the good you are importing. So, the importer has to pay the government that money in order for the product to legally come in to the country. The importer pays that cost, so the local purchaser pays that cost, so the consumer pays that cost. And each one of those (and likely many other) steps probably will add on a little extra for the trouble.

The hope is that encourages local production; even if it costs more to produce locally, when you factor in the cost of the tariffs to import, it might make sense to invest the cost to avoid the tariffs.

The troubles are:

1. you can’t often make a fully operational supply chain domestically in 4 years
2. the US doesn’t have some of those raw resources, like minerals or regional food sources
3. good or bad, places like China can pay professional factory workers way less than minimum US wage, which, in case this is news to anyone, is already far below a livable wage

Let’s not forget that the Republicans are an army of sycophants with zero capacity to think or act for themselves. Trump is a narcissistic pawn and absolute loser, but even at the highest level of power he’s only a problem because the Republican Party are either spineless cowards or deranged cultists.