Speed=Distance/Time
So if you divide the distance in km by the time in hours you get speed in km/h or if you divide the distance in m by the time in seconds you get speed in m/s etc.
Speed is a scalar quantity, meaning that it doesn't have a direction. 50 miles per hour could mean 50 miles per hour north, south, east or west. Velocity is speed plus a specifed direction, and it is much more useful than speed when it comes to physics. Velocity is a vector quantity, because it has magnitude and direction, so we can use it much more often than just speed.