Time is a coordinate on space time. It doesn't flow as a fundamental feature, any more than space flows. We have the impression that time flows because entropy is increasing, which gives us the arrow of time, whereas there's no arrow of space. The idea that we are propelled through time by some sense of flow is just a consequence of our macroscopic existence in a world where entropy is increasing. Entropy is a way for physicists to talk about the disorderliness, randomness, and disorganization of a system. The early universe near the Big Bang was very low entropy, organized, and non-random. Since then, it has been increasing in entropy. The universe creates more entropy by creating pockets of orderliness, like us. Entropy is a way of counting how many ways there are to arrange atoms without changing the overall look and feel of an object. The universe tends to move towards higher entropy configurations because there are more ways to be high entropy than to be low entropy.