The slow cooker, also known as a crock-pot, is a very handy appliance for many types of cooking. The classic image of use of a slow cooker is to load it up with ingredients and turn it on before leaving for work, and coming home to a dinner that is ready to eat. This actually works in many cases, but there can be a bit more to it than appears at first sight. The following information about slow cooking would no doubt be greatly amplified in a good slow cooker cookbook.
Slow cookers provide even, low heat, moist environment cooking. This can work well for many simple one dish meals. Beef stew is a good example of this.
You may be able to save money on meat by using a slow cooker. The low temp and constant moisture is a great way to tenderize cheap cuts of meat. The breakdown of collagen releases richer flavor than faster cooking methods.
Spending more money on a cooker gives the cook more options. The cheaper ones have a single heat setting; more money means more choices. Cooking on low is better for most dishes, but a higher heat can be used initially to get up to cooking temp faster.
Except for some top of the line models, the temperature settings control the amount of heat produced by the cooker. This indirectly determines the temperature. Some advanced models have controls that can be used to specify the heating time, and even stages, such as two hours on high followed by four hours on low. A few have temperature probes that can be used to actually specify cooking temperature.