I want to start a meal in my crock pot and the recipe only calls for about 4 hours of cooking. However, no one will be home for another 3 hours to turn it off, but it will shut down and go to the warm setting. Once it sets itself to warm, will it still be cooking? I don't want the chicken to be overcooked.
It's still going to be heated, so yes it's going to carry on cooking.
However, the temperature on the "warm" setting is going to be lower, so it will cook more slowly, and therefore you might be okay.
It's difficult to say for sure, because it depends on what exactly the temperatures involved are.
Yes, the "low" vs "high" settings on slow cookers are for different cooking times - really slow, or if you don't have that much time, the high setting.
If you look at the owner's manual, and the recipes in there, you can see that the dishes can be cooked on the low setting.
However, this assumes that you're talking about the low cook setting, and not an entirely different setting at altogether. The brand of slow-cooker might be helpful in this regard. Even in that case, if it's adding heat to keep it warm, it would still be cooking it to some degree.