First of all, if your dishwasher is older than a few years then it's probably not that high powered, and thus will not get off food that has been sitting on a plate in the sink for 5 days. The dishwasher is not some magical machine that sends out little scrub brushes to individually wash off the crusted mess on every dish.
First step: Rinse your fucking plate off.
Seriously. This is not hard. You're probably going to put it in the sink anyway so just rinse it off. If you happened to leave your plate out with food on it that is now crusted onto it: SCRUB IT OFF. Your shitty dishwasher will more than likely NOT do this for you. Also crusted on food sitting in the sink starts to smell after a while, and then no one wants to touch the dishes.
Second step: Put the dishes IN the dishwasher.
This seems to be the hardest step for some people, which is really fucking confusing because the dishwasher is normally right next to the sink. It's not like you have to go very far out of your way to open the dishwasher and put a dish in it. Seriously. Just fucking put it in there. If the dishwasher happens to be full of clean dishes: TAKE THEM OUT and then put your dish in there.
It doesn't really matter how you load your dishes in the dishwasher. I have my way, my roommates have theirs, my boyfriend has his. The only thing you need to remember while loading your dishwasher is this: Your dishwasher probably has some similar piece on the bottom rack to that circled in the picture below. DO NOT cover this. This is where the water spout thing comes out. If you cover this none of your dishes will get clean except maybe the one covering it.
Don't cover this. Seriously. Don't.
Step Three: Run the dishwasher.
This step is pretty easy. Just close the dishwasher and turn the dial to start it, or press the start button, or whatever your shitty dishwasher has.
You probably have some options on the front of your dishwasher. If your dishwasher is old/really shitty you should probably put it on pots and pans/pot scrubber/whatever just in case. I usually do heated dry too just because I like it.
Step Four: Empty the dishwasher.
This seems to be pretty difficult too. I don't know if it's a "I ran the dishwasher so the other person can empty it" thing, but when you don't empty the dishwasher you start the whole cycle of gross as fuck dishes piling up in your sink. Seriously. It takes less than 5 minutes to empty. Stop being a lazy fuck.
And there you have it. A whole guide on how to use your dishwasher. Now get off your computer and go clean up that mess in your sink.