The phase of a sinusoid only means anything when it is compared to something else or a reference.

So for example the phase of a wave coming through a capacitor is 90 degrees out of phase with a signal that doesn't, providing they started in phase to begin with. Similarly an inductor gives a 90 degree phase shift in the other direction. This is important because when you try and mix signals of different phases you get a reduction or increase in the final signal. For example two equal amplitude sin waves with a phase shift of 180 degrees will produce no output. The waves cancel. When they are in phase the waves add up and you get twice as much.

When you start to drive signals through circuits consisting of capacitors and inductors the situation is complicated but by using complex numbers to describe the waves the net result can be easily calculated. This is useful in designing things like filters.

And ultimately the universe is driven by complex numbers as quantum mechanics is entirely based on them.

Wrong way round, complex numbers describe what is happening in the universe, they don't drive it.