Evangelicals believe HARD in an end time prophecy and think jesus will personally hoover them up to heaven before bringing suffering to earth to punish the rest of us for our wicked ways. Evangelical think they are special. More special then everyone else. More important then anyone else. That's why they "know" jesus will personally rapture them to heaven and they are willing to kill humanity for the privilege. They really think they are god's favored and actively try to make certain events happen to move the prophecy along. They don't give a fuck about the future, or climate change, or preventing WWIII because in their minds the world ending is a good thing because it means jesus will come back - they want armageddon.

I grew up in an evangelical household. I was taught all the jews have to return to Isreal where they will die, the "good" christians will get raptured, and the rest of us heathens will earn hell on earth before dying horribly. They spend a large amount of time ruminating on this future they want to bring about. All religious sects have issues, but only one has a world ending death wish and has infested the US government which happens to have the biggest military on earth. That's a problem.

Watch the movie Bible Camp

Edit: it's actually called Jesus Camp

There's a lot of debate on that, if you want to get into the academic side. I think the best definition for it (when I was studying it in college) was based on four primary 'focuses' of evangelism. The wikipedia article on the scholar that laid them out explains them in brief: https://en.wikipedia.org/wiki/David_W._Bebbington
I've seen them cheekily laid out with the '-centrism' part in every one, as in 'biblicentric,' 'crucicentric,' 'conversioncentric,' and 'activity-centric.' The wikipedia page on evangelicalism itself is a pretty big slog, but talks more in depth about them.

What those four things mean in practice is very interesting, again in an academic manner, in how neatly they lay the groundwork for MAGA/this shit we're seeing. The biblicentric primes them to reject the authority of more 'traditional' sects when there exists conflict between beliefs (even between different evangelical churches), because the bible is 'always right' and you can always find something in the bible to contradict something someone is saying, and is a major part of why evangelicals that move will church shop for a while (so they can find one that fits with their beliefs, highlighting, of course, that their beliefs are not necessarily based on much more than vibes). Crucicentrism isn't as big, but it's a part of their 'us vs. them' mentality that pops up. The emphasis on conversions and activism is part and parcel of why so many of them want to force their beliefs on others (think abortion bans and such).

Now take those religious aspects, and throw them at politics (where politicians specifically target them). They're already primed to reject logic, even christian logic, so republican (well, fox news style propaganda even more so) calls to reject what the other side says finds fertile ground. Use their desire to spread their beliefs in controlling, political manners, and you've roped in every one of them that wants to 'do christianity' with all the guilt they have built in about not improving anything suddenly being assuaged.

With white evangelicals, it's racism, xenophobia (big overlap there) and misogyny.

In theory, it's a subset of Protestantism that's more concerned with evangelism (sharing the gospel and converting others), as well as a couple of other doctrinal distinctions, than the "Mainline." Evangelicals and Mainline together make up Protestants; Protestants, Orthodox, and Catholics together make up Christians.

In practice, at least in the US, "evangelical" seems to have come to mean "activist;" as in, politically right-wing.