Bitmaps are basic image files that are commonly used on the Internet. They are composed of dozens of small, colored squares known as pixels, which when seen from a distance appear to form a smooth image. If you zoom in enough, you can distinguish the individual pixels which compose the picture. Because of their popularity, bitmaps can be viewed by native software in both Windows and Macs. This makes opening and viewing them as easy as a couple of mouse clicks.
Double-click on the bitmap file if you simple wish to view it. Without additional software installed, Windows will automatically open the BMP file in Microsoft Windows Photo Gallery Viewer. Likewise, Macs will open BMPs in Apple Preview.
If you wish to edit the BMP rather than just view it, first open image editing software such as Photoshop, PaintShop, or GIMP. If you don't already own image editing software, you can freely download and install GIMP. Likewise, Photoshop and PaintShop have fee trail versions, though you will have to pay for them after the trail period has ended.
Click "File" and then "Open." Click on the BMP you wish to edit and then click "Open." This will load the bitmap into your program so that you can edit it.