Reality
Results in quantum mechanics show that reality is not inherently real. Reality exists as a superposition of different posibilities. Like a foam of the different possible states all coexisting at the same time. Measurement collapses this reality into one of the different posibilities. And furthermore, the way the measurement is realized will influence its result. Making some posibilities more likely to happen than others. This is known as the observer effect. Theres nothing stating that superpositions stop at small scales. As above so below. It also does not stop at the observer, and the observer itself can also be in a superposition with regard to a secondary observer. Even more interseting, two observers measuring the same phenomenon can be in a superposition with regard to one another and their mesurement until they both compare their results. Some traditions consider reality as being mental and part of a consciousness field that extends everywhere.
Perception
The human brain seems to be capable of influencing quantum events. Experiments have shown that the human mind can influence random events via attention. By focusing, participants could influence the Brownian motion of a particle. Others results showed that participants could slightly influence the results generated by random number generators. These is not negiglabe and indicate that the human mind can influence reality.
The way our brain measures reality is via our senses. Perception occurs subconsciously and will depend on the subconcious beliefs of the observer to give it shape. Our concious observer is just a passanger to what our subconcious has already mapped.
Our beliefs shape reality. What we expect to see change what we “see”. As mentioned before, we are in a superposition with respect to other observers. Reality is measured in paralel by all conciousness. So the agregate sum of the beliefs of each individual is what generates our common shared "reality", this is commonly called the "collective unconcious".
Disclosure: The writer's bias is more inclined to believe scientific or pseudo-scientific explanations; therefore, he has chosen to talk about these topics in terms of the subconscious mind and the observer effect. The same conclusions can be reached when exploring different systems of belief. This same phenomenon that we call the subconscious mind can also be called god or your “higher self” without changing the bottom line. This means that the explanations offered here are independent of your belief system.
Changing Reality
There are methods to change your beliefs and modify your reality. The rational part of the brain is constantly filtering the information that gets to the unconscious mind. This makes it hard to directly change what the subconcious mind believes. This is why different traditions have created methods to "distract" or "bypass" the rational brain. This include things like: meditation, sigil magic, ritual magic, prayer, alchemy , afirmations, memes, hemi sync. The purpose of all of these methods is to implant beliefs into the subconscious when the rational mind is either exhausted or distracted and therefore most likely to let beliefs pass through unchallenged. By making use of these altered states of mind,you can implant believes that more closely align to what is important to you.
Unfortunately, since reality is a common effort, others have to share your vision of reality for it to manifest. They have to agree or at least see it as possible. You would have to have a strong will to be able to override the reality of others. But change the beliefs of enough people and you can impose your vision of reality. How they perceive you can help you, this is best resumed by the common trope of "fake it until you make it".
A word of warning
Your mind is a battlefield. Different groups are fighting for your attention and for access into your subconcious. By changing your beliefs and that of others, they are able to ground their vision of reality. Groups like governments, corporations, religions will use all sort of techniques to impose their own vision of reality on you. Our desires, our beliefs have been feed to us without our choosing. Mass media for example,chooses the narratives are to direct our attention and implant beliefs into us. They are not concerned with showing you the truth, but instead with choosing what you focus on. Incresingly negative news will create a feedback loop by influencing the beliefs of its readers and manifesting the reality that they show. Be wary dear reader of anything you consume, discard anything that doesn’t serve your porpuse and tries to influence the way you view reality. You have the power to choose what is really important to you and your loved ones, do not be your priorities be given to you by those with power. Make sure that whatever matters to you is what you focus on. We create reality and we should all take an active involvement in this process. A lot of us have become lazy and complacent, letting reality be fed to us, we are too comfortable. Humans are programable, either you can programmed reality or be programmed yourself.
How does this work in practice ?
Lets say its saturday night and youre watching a movie on tv, you start to relax and you become more susceptible to subconcious messaging. Then when ads play during the break. Your brain in its relaxed state will be more suspceptible to its messaging. This is the main show, the movie is just an excuse for you to lower your defenses and be fed the propaganda. Though of course, the movie itself also imposes a certain world view on you.
I would also like to extend a warning against social networks. They will feed you content that can influence the way you act and your desires. Their algorithms is made to keep your attention and direct it. If a company or a goverment pays them, they can start feeding you content that will promote views benefiting them.