@MODS: Hello, hello, hello! I am excited about this cause I actually have an answer, I actually know what I am talking about so please don't remove this but instead ask me to clarify which I will gladly do!

Now, onto existence and reality. The first thing many philosophers ask is how do you know that you really exist? Since we're questioning reality we should question your existence too. Descartes discussed you existing during his meditations, he came to conclusions about your existence and the existence of reality. Even though he thinks he made a good point for reality being the way it appears, his arguments have been torn apart over time so I will only talk about the one most people know "cogito ergo sum" or "I think therefore I am". The argument goes as thus: You do not know if what you are experiencing is real or reality, however you know that you are experiencing it and thinking about it. Because you are thinking there must be something creating that thought, even if it is a brain in a vat being tricked into believing nonsense or you're asleep and this is all a dream, if you are thinking something is making that thought and therefore "you" (the thing making the thoughts) must exist in some form.

Now onto the rest of reality. Dewey in his "essays in experimental logic" talks a lot about what truth and knowledge are but we don't need that right now. Dewey addresses the old question of "what if all my senses are lying to me and nothing is as it seems" by claiming that the question itself proves that there is a reality. If your senses are being tricked then having senses are a premise to the question, and so is the fact that your senses must receive some input from somewhere that is misinterpreted. The fact that you have senses that can take input and input coming in shows that something exists outside of you, and that thing is reality. There is no telling what this reality can be though, you could be a brain in a vat hallucinating reading this reddit comment, in this case "reality" would be the vat and the world outside the vat while all this is a figment of your imagination.

If you are perchance asking if we can ever know if anything is real, the short answer is no and the long answer is it does not matter. Many pragmatists and Hume, he is not officially a pragmatist though I will argue that he is, say that we can never be 100% certain of anything. That is to say, we can not prove that reality will continue to behave the same way for the rest of time. Hume does a great job of proving this by showing how all we have is proof by induction, which I can explain more but I do not think it is useful here. These philosophers (hume, james, dewey, and others) say that it is ok that we can not know a fact with absolute certainty. A massive summary of this view is that even if we are tricked into believing a false reality, that is ok because we can continue existing and gaining practical, useful results from this reality