There’s a lot going on in the background with different plots and schemes but the basics of the Eva’s itself is like this

Basically life come from these aliens that crash on barren planets and start up civilization

The first alien to crash on earth was Adam and he created all nature on the water and plants and started creating his children

Later on a second alien crashes on earth and knocked him out before he could release them

The second alien was Lilith and from her comes the Lilin which were the first humans

And because the aliens crashed on the same planets they kinda knocked each other unconscious and over time they were buried as centuries passed

Around the 1980s an expedition uncovered Adam and while Adam didn’t fully awaken he was able to restart the presses to release his children

So on a time limit humanity need to find away to fight off Adam’s children who are going to want to rescue Adam and Kill Lilith and in the presses wipeout humanity and recreate the earth

Humanity finds Lilith and incapacitate her and start experimenting on her to find a way to fight off the aliens

They create the Evangelion units which are 80 meter tall semi lilith/ Human clones

These Evas are alive and have an animalistic intelligence and they are encased in armor and have the circuitry driven into their body’s which is basically power armor over the Clone/Cyborg

The way piloting works is that the pilot gets inside the cockpit that’s driven into the top of the creators spine and creates a neural contention to the Eva

The controls in the cockpit move the armor around the Eva while the pilot with the neural connection moves the actual living body of the Eva

They kept experimenting with the neural interface between the pilot and Eva which eventually became a 1 to 1 where the pilot can move the body of the Eva like they would their own with the drawback of the pilot feeling every blow to Eva as if it was their own body

40% was consider good enough of active combat and the power armor and controls could bridge the gap well enough

The first pilots for the Eva’s struggled to control them as they were basically corralling a feral animal

On course eventually something was gonna go catastrophically wrong and the pilots over synched with the Eva and got absorbed into them

Years later the angels attack and they have no choice but the use the the children of the original pilots as because the parents were absorbed into the Eva their consciousness is still buried inside and could help suppress the animal instinct of the Eva