Paint — windowssystem32mspaint.exe
Start → All Programs → Accessories → Paint
Paint is a basic image editor (often called a "paint program"), capable of creating and modifying most .bmp, .jpg, .gif, .tif, and .png image files.
At the bottom of the window, you'll see a color palette; the left-most box shows the currently selected foreground and background colors. To the left of the document area is a simple toolbox. Each tool has a different function used to manipulate the image in some way, the use of which should be fairly self-evident.