I don't see the connection between those 2 sentences.If that is the case, how is it possible to throw anything?
But to explain throwing - initially the stone is at rest in your hand. You then accelerate your hand to say 10 m/s (the acceleration determined by how far your hand moves, if it's 1 m uniform acceleration it's 50 m/s^2). You release it, and it's then subject to constant downward acceleration g, so it rises for a while, slowing down, stops and falls back down.