Composting

If you read my top-level comment, you'll see I'm not a big fan of this infographic. It makes composting out to be way more complicated than it actually is, and implies that composting is like a cooking recipe: leave out one ingredient or add something at the wrong time and the whole thing turns out wrong. For instance, I've never added grass clippings (no lawn), shredded paper/cardboard* (don't trust it to be chemical-free), or soil (except soil stuck to dead plant roots; I've read it slows down the composting process) to my compost bin.

At my house, stuff goes in the compost bin as it's available: kitchen scraps as they're produced, garden waste as the seasons change and I swap out plants for the next round of crops, etc. I do maintain a box of brown matter so I can sprinkle some in from time to time to keep the bin from getting too smelly. I definitely don't add the "correct" ratio of green:brown matter as I produce way more of the former than the latter, and I'm not about to go out and obtain more materials just for the sake of keeping my compost balance perfect. Someday when I'm not renting and have more space than my current postage stamp yard and more control over my yard, I want to produce better compost with more balanced ingredients, better temperature regulation, and more regular turning so I can create a more self-sufficient garden that doesn't require buying dozens of bags of compost every year. However even working within my current constrained situation I've managed to keep a massive amount of organic matter out of the trash bin, and even produce some enrichment I can add to my less fussy plants' soil.

tl;dr: the layers are not actually important in practice, but they make for a nice, clean infographic. If you're new to composting, the most important thing is to just focus on what is/is not compostable.

It's really just that it 1. makes it easy to judge that you have a good ratio, and 2. gives you a start to intermixing them. You really shouldn't leave it in layers, except maybe to have some dry stuff on top to help keep it from drying out. Mix as thoroughly as is reasonable.