Calculating Transistor Parameters
Vcesat is a saturation voltage of the transistor - when the transistor will be on, there will be no more than 1.2V voltage drop over it at 1A current. So you have to have at least 9.5 + 1.2 = 10.7V supply voltage.

Now the current. Graphs on page 5 of datasheet show current gain of 500 at 1A. This means you need at least 1A/500=2mA of base current. There will be a 2.8V drop over base emitter when transistor is on - Vbe(on), take this into account when you calculate the resistor value. 

To make sure you are switching the transistor on really hard, you want to run the base at somewhat 5 - 10 times the current (10 to 20mA), note Vbe in this case will be at 4V.

To provide more specific information we need to know your supply voltage and the voltage you are switching the transistor on with (microcontroller? 5V, 3.3V?)