Question

how did electrons pass through the barrier of quantum tunneling?

Answer 1

When an electron's probability wave encounters a potential barrier, instead of ceasing to exist (classically), it decay's exponentially throughout the barrier. On the other side of the barrier, the probability wave will continue to exist, although at a much smaller magnitude. As a result, an electron or particle can exist outside of a potential wall.
http://en.wikipedia.org/wiki/Quantum_tunnelling

Answer 2

but how does it actually tunnel through has this got to do with the energy it has like since it has so much energy it can pass through?

Answer 3

You're still thinking too classically in terms of how electrons or particles behave. Instead of an electron orbiting a nucleus, think of it as existing throughout a cloud region surrounding the nucleus. The edges of this "cloud" are actually limitless, but the probability of finding the electron diminishes greatly as you get farther and farther from the nucleus. So instead of saying "the electron is moving along this path here", you would instead say "the electron is somewhere in this imaginary sphere at a given time, and the next millisecond it could be anywhere else, as opposed to next to where it used to be, travelling in a orbital path."
Now remember, while I say "spherical," this sphere doesn't have a radius, but instead the electron has a probability of existing in areas of this "sphere", with some areas being more probable than others (as you get farther away from the nucleus). As a result, while the electron is classically just supposed to orbit the nucleus, it can actually exist anywhere in the universe at any time, although the probability is virtually negligible, hence why I can't teleport through walls. Now while the electron can't exist where another atom is IN a wall, it can exist on the other side, simply with an even lower probability.