There are two forms of truth, one that is true because you believe it to be true, and one that is true no matter what you believe.
The first form of truth comes into existence through your actions. By acting upon the world and behaving as though a belief were true, you create patterns and consistencies in the Universe based on this truth, and others that interact with these elements will find them truthful in that sense. In this way you, the subject creates subjective truth, with which you can build around it a system that is only understood by following said truths.
The second form of truth is objective reality. It underlies all subjective beliefs to the extent that all subjective things touch on or are referencing directly or indirectly, something that exists. However, the subject can never be certain that their beliefs are exactly as the real.