Soil
There is a good reason to start with the soil. Apart from it being the interface between seed and plant - The part you're most interested in if you're into plants. It's literally the engine of the garden.
This is why you have to create good soil before anything else will happen. No soil, no seed germination. No soil, no nutrient or substrate for seeds to grow in. No soil, No good.
Now you could go to the local garden centre and buy a bag… a plastic bag… a petroleum-based polymer bag that holds soil created offsite.
You could decompose yourself a bunch of food scraps.
You could even go and collect a bunch of leaves from the local park.
These 2 options centralise around the concept of building soil from scratch. Which is literally what a forest does. A forest does not do debit cards or car rides to crop swaps (which I actually think is a good idea). It grows everything it needs… including soil.
But notice that nothing requires you to actually grow anything. Like a forest, your garden can tap into what some would consider “waste” streams.
Scraps and leaves are free. People (and maybe even yourself up until now) are literally throwing that stuff out. Like it was yesterday's news. I’m telling you… it's hot off the press. Tomorrow's sensational scoop.

There are 2 common methods of building soil from scratch.

Composting and Worm Farming.

Both are stupid easy to do.

With a little practice, you can be shoveling soil into your desired ditch in no time at all.
With a little bit of expertise, you can be harvesting nutrient-dense seed substrate at hyperspeeds.

--------- @mr.betteridge