What is brexit about? i am an ignorant american, teach me

The reasons for Brexit really depend on who you ask.
My take on it: former Prime Minister David Cameron made an election promise to hold a referendum on leaving the EU. He had been pretty sure it would come to nothing. I might add he was also a pretty unpopular Prime Minister. The polls showed that a significant number of people did want to leave, and Cameron panicked and sent out an 'information leaflet' on why we should remain in it. Many people voted Brexit out of spite against the government, and the propaganda only stoked up their anger further - especially since it was funded by the taxpayer. Thousands even sent their propaganda leaflet back to Downing Street in protest.

Some people voted Brexit because they don't like the EU as an institution. These are often older folk who have seen how the EU has changed over the years and feel like they've gone from having a merely economic agreement between countries, to being lorded over by a non-democratic form of government they had never asked for. Some are afraid that the EU will try to become a super state. Some folk don't like the way the ideology of the EU is being subtly imposed on the country. These people might be religious, or right wing, or might just have some really rad ideas that don't sit well with the political correctness police, and they don't want to have any more ideologues over them dictating what they are and aren't supposed to believe, than they need to have.

Some people think that immigration is the biggest source of the UK's social and economic problems and were given the impression (esp. by the Far Right) that leaving the EU would solve this. The thing is, the immigrants who tend to be scapegoated, don't tend to be European. Still, that didn't stop the voters from being fooled. Some pro-Brexit politicians even suggested that the money that stood to be saved from not being in the EU might be contributed to the NHS (Britain's state-funded health service) instead. It sounds laughable now on multiple counts, but at the time some people were taken in by it.

People who voted Remain tend to tar those who voted Leave with the brush of intolerance and hatred of immigrants, or accuse them of simple stupidity. I actually think that the reasons people voted remain are more complex than that. The largest age group in the UK is baby boomers and they were the group most likely to vote leave, whereas people of my generation mostly voted Remain. Baby boomers might be less cosmopolitan than us, but they're not just some big stupid racist mass - not the majority of the biggest demographic segment of the population. I can't help but wonder what that generation has seen which we haven't seen. Such a large proportion of them voted Leave, and dismissing them as 'racist old fogeys who don't know anything' may be tempting but what we've got on our hands is far too important to be that superficial about. It's true that my generation got all the cushy EU member benefits, like Erasmus and school exchanges and so forth, and we like travelling and are much more likely to settle abroad than our parents did. But staying in or leaving the EU is about the whole country; way more has to come into it than perks and freebies.

Cameron resigned as PM after the Brexit vote and Theresa May took his place. She is determined to make Brexit happen, despite not personally wanting it, because of what it would mean for democracy if the referendum result was not upheld (or so she says). The situation has turned into a complete shambles because the country voted Leave, without knowing what that would entail. In effect, they had no idea what they were actually voting for, and voting 'Leave' was essentially a blank cheque for 'anything but the EU'. And 'anything' covers an awful lot of things. Nobody had any idea of the trouble that casting that vote was going to cause, and many people hadn't even believed that their vote was going to be taken seriously, thinking 'It'll never happen'. There is a spirit of apathy about voting in the UK and the received idea that 'nothing will change - they're all as bad as each other.' Many people in the UK, especially the poor, aren't used to their votes resulting in positively perceived change; it's just a symbolic act of doing your democratic duty. So they weren't really aware of the weight that their referendum vote was going to have: voting always was a symbolic act that didn't change anything, so what was the difference with a referendum? Some of them were so ignorant they didn't even know what the EU was or what it did; they just hated Cameron telling them how to vote.

A majority may have voted to leave the EU, but only a very small number, if anyone, had wished the present crisis on the country.

Being politically correct is what people want others to do.

It's 3 of the 5 mentioned.

You could just look it up