I have always read and heard about the quantum theory but have not been able to grasp it enough, what would you say is actually the quantum theory

I'd say a couple of things present themselves as very fundamental and intrinsically quantum (non-classical.)

1) Finiteness of the quantum of action (quantities such as energy x time, momentum x displacement, angular momentum)

2) The need to express probabilities in terms of a more primitive quantity called the probability amplitude, which is complex.

But it's impossible to explain quantum mechanics in a few sentences and without mathematics.

Everything is actually a wave, with certain discrete behaviors when we observe them.