I believe that the scientific method as the best way to determine how the world works. Saying that I "believe in" evolution implies that it is some kind of religious philosophy.
It is a continuous set of gradual changes. I'm not so sure that "cycle" is the best term, as that implies a repeating process, like the water cycle.
I'm not sure what you mean by repeating itself. Evolution is a continuous process that has been going on for an incomprehensible length of time, and has not stopped. There is no reason to expect that human beings are the end result and that evolution is therefore finished. There is some evidence, in fact, that human evolution is accelerating.
The evolution you're talking about is a gradual change, and yes, hominids from 4 million years ago are more primitive - meaning less like modern humans - than are ones from 2 million years ago.
Here is some information about the evolution of hominids.
Mostly, when people try to refute the theory of Evolution, it is based on an insistence that the Bible must be taken literally, or on a lack of understanding of what evolution is all about.
There is nothing in the theory of evolution that disproves the existence of god. It does run contrary to the idea of taking the Bible literally and insisting that the Earth is only a few thousand years old, and the humans and dinosaurs once co existed. That notion is no more supportable than is the geocentric model of the universe.
Here is an explanation of the terms.