There are plenty of tutorials on line so I'm not going to explain in detail. However, the one difficult issue might be getting the ball count right. The easiest way is to assemble the spindle in either cup in your hand. With everything dry, put the spindle in far enough to close the hole and feed balls under the lip. When you think it's right, drop the spindle down so it pushes the balls into the tracks and turn in and see if you have enough balls with small spaces between (total free space is less than one ball's width).

With dry trial and error assembly you'll quickly know exactly the right number of balls, and cannot screw it up when you assemble the same into the bike.