Okay, how do you turn colour pictures monochromatic? Because I need to do it for a school project.

The quickest way to get black and white is just to select:

Image->Mode->Grayscale

it turns a color image into a grayscale. Another way to do it is to use:

Image->Adjustments->Hue/Saturation

and take the Saturation control down to 0. If you want to play around with monochrome that's other than black and white, use the Hue/Saturation dialog and click Colorize on. Then play around with the Hue and Saturation sliders until you get something you like.