What about *you*?? Do you exist?? As far as I'm concerned, you might just be part of some dream I'm having.
Unfortunately, none of this can be proven beyond a doubt to truly exist. We have to accept these things without proof.
The only thing you will ever be able to truly know without question is this: *something* exists. The exact nature of that something you can never be 100% sure - but, since you are having thoughts, then something exists.
Rene Descarte wrote about this so much more eloquently than I could possibly hope for. He wrote the famous line, "I am thinking, therefore I exist". The Latin phrase for this is well known: "Cogito ergo sum"
From the Wikipedia article about his philosophical proposition: "The simple meaning of the phrase is that someone wondering whether or not he exists is, in and of itself, proof that he does exist – at the very least, there must be an "I" who does the thinking"