There are three way converting your shot into black and white using photoshop.
Grayscale (go image>mode>grayscale)
Channel mixer (go image>adjustment>channel mixer)
Desaturation (go image>adjustment>Hue/saturation)
Grayscale The Grayscale method is a straight away change the image into B&W by just simply clicking on the grayscale button.This is the simple way of turning your photos into B&W.But not much adjustment you can do when using grayscale.
Desaturation This method also similar with Grayscale but not so very straight foward as the grayscale way. By using the slider on the saturation. Slide it to the left Negative (-) to desaturated the color. Using this method also you can control the RGB by changing it on a drop down menu on top of the Hue/Saturation bar window. Channel Mixer The best way i've discovered in converting your shot into black and white is by using Channel Mixer where you can still control the RGB event after it has been converted into monochrome. You can adjust the Red, Blue and Green in making the image more punchy B&W shot. When adjusting the RGB, make sure the number as close as it get to 100. so that you will not blown so much on the highlight and also the shadow.
Do a little bit of experiment then you will understand it better, just make you save it as a new image in different file so that you will not change the original image.