Control a 3W RGB LED with an Arduino
First off, note that the LEDs you have chosen have a pad on the back side:

That pad must be soldered, and it must go to a large metal surface on your circuit board.  High power LEDs can get hot.  The metal helps to radiate the heat away and keep the LEDs cool(er.)
If you don't do that, your LEDs will not live long at full power.
It is not clear if the thermal pad is connected to one of the other pins.  Without a note in the &quot;datasheet&quot; (that web page hardly deserves the name) I would assume it isn't connected.  If you already have them, check all the pins against the pad with an ohmmeter and see if the pad is connected to anything.  It might be connected to the + pin.
As to driving the LEDs:
The simplest is to use a standard pulse width modulation circuit and a series resistor.  That's probably not the best, but certainly the simplest to achieve with limited parts.
This is a simple circuit to drive one LED:



simulate this circuit &ndash; Schematic created using CircuitLab
PWM comes from your Arduino.  That's a digital signal that switches on and off for a variable time.  It comes from the misnamed Arduino &quot;analogWrite&quot; command.
You will need three of those for each 3 color LED you want to drive - one circuit for each color.
You have to calculate the resistor value from the maximum current you want to use, and the approximate forward voltage.  You use the worst case forward voltage - that's the lower one.
$$R = \frac{V_{supply}-V_f} {I_{maximum}} $$
Assuming a power supply of 5V, and a maximum current of 300 milliamperes, you get the following resistors:




Color
\$V_f\$
Resistor (ohms)
R (Adjusted for brightness)




Red
2.0
10
26.7


Green
3.0
6.7
26.8


Blue
3.0
6.7
6.7




I've included an adjustment for the relative brightness (luminous flux as the datasheet calls it) to make the full on brightness of the LEDs come out somewhat close.
The full circuit for one LED would look like this:



simulate this circuit
The red and green LEDs won't get as much current as the blue one, but they should be somewhat closer in brightness due to the different resistors.
You'll have to pick resistors rated for the dissipated power.  The resistor for blue will dissipate the most power. That's \$ P =\frac {V_{supply}-V_f} {R} \times ({V_{supply}-V_f}) = 0.6 watts.\$  You'll want to use resistors rated for at least 1 watt.
You drive each PWM pin with an analogWrite command.  It will take three pins to control all three colors of one LED.
All on, fully bright, close to white:
analogWrite(PWM_Red,255);
analogWrite(PWM_Green,255);
analogWrite(PWM_Blue,255);

All off:
analogWrite(PWM_Red,0);
analogWrite(PWM_Green,0);
analogWrite(PWM_Blue,0);

Blue:
analogWrite(PWM_Red,0);
analogWrite(PWM_Green,0);
analogWrite(PWM_Blue,255);