The first thing to do is get the photos you want to work with onto the computer. If your source is a digital camera there is little problem. If starting with actual photos then there are two routes. You can scan prints using a flat-bed scanner. Nearly all modern scanners produce very good quality and are easy to use.
Some scanners offer transparency adaptors as optional extras for scanning slides and negatives.
If you have one of these you probably don't need us to tell you how to use it. These give extremely high-quality images and are a very convienent medium for using with a computer. For overall quality, 35mm film processed to CD is almost always best. Few, if any, digital cameras are as good. Scanned prints give surprisingly good quality, surpassing a lot of the cheaper digital cameras.