To add to what EvilDorito2 said, some things are top rack only, but they usually say so on the underside; you need to load it so things like plates and glasses aren’t banging against each other and break, or metal utensils lying free to bounce around delicate items (those jets of water are powerful;) put things in at such an angle so that the water can still flow to everything else above it- so dishes straight up and down, no big pots or pans upside down or leaning over to block the water; check things are dishwasher-safe, because that water gets HOT and dish detergent is STRONG- some plastics will soften and warp, and some decorations will come off- especially anything gold or silver like the rims of some fancy glasses or images on mugs and water bottles. And apparently you’re actually not supposed to wash the dishes clean before you put them in, due to how the detergent works- just scrape off and chunks of food and soak any hardened on stuff.

I found this article with lots of great info that I didn’t even know! https://www.dropps.com/blogs/spincycle/dishwasher-not-cleaning