Of course you need a using System. Once you have a graphics object you can use it to draw using a collection of other objects and methods that anyone familiar with the GDI API would probably recognise. For example, there are pen and brush objects, which set the outline and fill properties for the graphics object. Many of the drawing methods accept a pen or brush as parameters. For example, SystemPens.
Control gives a pen used to draw the outline colour of a button or control and so on.
You can also specify colours using the Color structure. The Color structure has properties A,B,G and R allowing you to set a colour directly. All colour components are 8-bit values making a full colour specification 32 bits. The only minor complication is that the Brush class is abstract and only really used to define reference variables that point at particular instances of classes derived from Brush. At this point getting to know the graphics class is mostly a matter of discovering what drawing methods it has.