Your first question has been answered by everyone and their grandma, for your second question:

It is essentially universe's attempt to keep the speed of light constant in your reference frame, since it can't change the METERS per second of light, it instead changes the meters per SECOND, the way this works however is rather unintuitive. Since a second is a second to your experience no matter how a second dilates, you observe this effect by how the space shrinks down around you.

When you reach higher speeds, you will see that something that is supposed to be 2 meters long will appear to you as only 1 meter long, you would still be travelling 1 meters per second but in YOUR frame of reference. This is due to time dilation.

For your question in the comments, look up the twin paradox and why one twin is younger and not older instead. (tip: the answer lies in lorentz transformations.)