If YouTube isn't blocked, watch this great video series by ThreeBlueOneBrown. (link later)
If YouTube is blocked, here's a quick rundown:
AIs are powered by neural networks, like our brains!
In an AI, a neural network is made up of Neurons, which are nodes connected together by a connection.
Each Neuron has a value stored for the other neurons in two variables, weight and bias.
To train the AI, You start with a bunch of "brains" with random values, then pick one of the best performing, and "kill off" the rest. Then, you make a bunch of copies of the best performing one, with some random alterations. Then, you repeat the process all over again, with the new brains.
(This is from memory, and is probably wrong someway.)
An "Actual AI" is the same thing, but with a huge supercomputer behind it, and trillions of neurons.