Question: How many things are there? Answer: either "one", "an infinite number", or "both one and an infinite number".

If you answer "one" or "both one and an infinite number" , then you've got the concept of oneness. The first view focuses on one entity containing all, and the latter focuses on all contained within one, which are mirror images of the same view. I personally believe that the former "one" view is most efficient and effective in mastering life. What is unitary (not separated) does not need to be integrated. Integration is difficult unless the components were formed with integration in mind.

To express a unitary view, all you need is to express your understanding of oneness, and all that it contains, in thought, word, and deed. With diligence, you can achieve full expression of oneness in you life.

If you answered "an infinite number" to the original question, then you're taking the majority view of our species.

The common sense-based belief in separation is present despite the evidence to the contrary from the physical sciences (physics, chemistry, biology, ecology, evolution etc.), social sciences (organization, economics, government, politics, etc.), and ancient beliefs.

It is easy for us to be misled by our body-senses, and to be confused about the terms "separate" and "different". These sense-messages easily give rise to incomplete beliefs that things are unconnected, with accompanying thoughts, words, deeds.

When you say an infinite number of things exist in the universe, you're recognizing that there are differences between things.  Differentiation is a fundamental characteristic of the universe.  But individual or type difference does not indicate separation from a common root.  Nothing is truly alien to us, when seen from the perspective of one universe, contained within something even larger (which we are just beginning to see).  For practical purposes, we can believe that all of the different things in the universe are interconnected within a single thing, the one universe.   If you use the analogy of a family tree, everything sprang from one creative activity.

Distinctive difference is as important in the universe as it is in our bodies. As an illustration, what would be the effect on your body if there were no differences between cells? Answer: your body would be composed of undifferentiated cells, resulting in no heart, no lungs, no brain, no eyes, etc., putting our bodies on the same level as the simplest multicellular organisms. If you can carry this awareness of the importance of differentiation and the resultant diversity to other life forms, other physical forms, or other social, ethnic, national, political, and economic forms, then you're on your way to understanding oneness.

Thus there is no actual separation between things, only branches of variations on a theme rooted in the universe. There are principals and forces binding together the different components of the universe in ways that we are just beginning to grasp with our sciences and our minds. Research the physics of Bohm's "Implicate Order", Bell's "non-locality", or the Zero Point Force (ZPF) to see where our sciences are pointing us.

I hope you learn why either answer that contains "one" is true, while the answer "an infinite number" is false.