Can any body explain me what is a Context and how can i use it? There is also Graphics Context (CGContextRef).Is there any relation between Context and Graphics Context?
Likely you're talking about the same thing in both cases. From the Quartz 2D Programming Guide:
A graphics context is an opaque data type (CGContextRef) that encapsulates the information Quartz uses to draw images to an output device, such as a PDF file, a bitmap, or a window on a display. The information inside a graphics context includes graphics drawing parameters and a device-specific representation of the paint on the page. All objects in Quartz are drawn to, or contained by, a graphics context.
You can think of a graphics context as a drawing destination, as shown in Figure 1-2. When you draw with Quartz, all device-specific characteristics are contained within the specific type of graphics context you use. In other words, you can draw the same image to a different device simply by providing a different graphics context to the same sequence of Quartz drawing routines. You do not need to perform any device-specific calculations; Quartz does it for you.
There is another definition for the word context in CS, but I think the above definition is what you're looking for.