If there is a set of identical twins, and one of them gets into a spacecraft and travels at 99.9% the speed of light, for what seems like 25 years here on earth. (Assuming that there is such a spacecraft, of course.) If he travels at that speed and returns to the earth, his twin would be a lot older, but he would have aged only a little. So the one who travelled will look almost just like before, but the one who stayed back would have grey hair, and other signs of old age. In their minds also, the one back on earth would have felt 25 years passing by, but the one who travelled would have only felt a few days go by. But both of them, when they meet, will be in the "present" - the traveller would not be in future. They would be able to shake hands and interact with each other, which would not be possible if one of them had travelled in time and gone "away" in time. (The numbers I gave are only to illustrate the point - to get the real figures, you would have to do a Lorentz transformation, which is pretty easy.)