There is a wealth of info on the web about slow cookers but I'm going to share here the tips that have helped me most.
I'm gonna assume you're a slow cooker novice, so I'll start from scratch.
What does a slow cooker do? A slow cooker cooks food slowly, obviously. The main advantage is that your food can't burn nor does it need stirring/watching. You can leave it on all day while you go about your business, go to work etc and come home to a cooked meal.
Why slow cook? For me I want to spend my time playing with my kids. I don't want to be running in and out of the kitchen stirring a sauce or checking the oven, so it is a lot less labour intensive.
It also saves money. Apart from the initial cost of purchase the slow cooker uses less energy than the normal oven. We all like saving money.
What can you actually cook in it? I've made pasta bake in my slow cooker. I've cooked soup, stew, casseroles, roast vegetables, cinnamon rolls, fudge, chilli... When I bought the slow cooker I was initially concerned about finding enough vegetarian recipes for it as most recipes online included meat but I have found that I can adapt most of our favorite meals for the slow cooker. It seems to work best with root vegetables. We had a dodgy batch of cauliflower cheese which taught me dairy and cauliflower don't lend themselves to slow-cooking.
Another great tip I learned is that any liquid added gives you a soup. Slow cooking releases the water in your food and traps the steam, so most dishes need less liquid than usual. For example I made a ratatouille in it and instead of a tin of chopped tomatoes, the recipe called for tomato puree. Enough water came out of the aubergine to keep it moist.
Lifting the lid of the slow cooker adds 20 to 30 minutes extra cooking time. Also it works best at 1/2 to 2/3 capacity. Just yesterday I filled it three quarters full with a potato dish and it took at least 3 hours extra cooking time. (Too full plus lifted lid 3 times) Just as well I had begun it the night before, eh?
These are my first lot of tips for slow cooking, please add any of yours in the comments, I'd love to hear how you use your SC.