How To Make Shoes

1
Make a custom last. A last is a block in the shape of a human foot shoemakers use to guide their work. To do this, you'll want to make a cast mould of your foot; that way, the shoes you'll be making will be custom-fitted for you personally. Get a box filled with an alginate jelly and place your foot in, ideally up to the ankle. Let your foot rest for 20 minutes while the jelly solidifies, then slowly remove your foot. ^[1]

Make sure to remove your foot slowly; you don't want to damage anything once it solidifies.
It's highly recommended you do this for both feet at the same time. The idle time is best to get over with early on in the process.
One positive thing to mention about this step in the process is that you can ideally reuse these lasts for each subsequent pair of shoes you try to make. Make a point of keeping them somewhere safe, where they don't run the risk of being broken.

2
Pour casting material into your casting box. Now that there's a proper mould of your foot, you can pour casting material into it. Depending on the type and quality of casting material, the solidifying time could take anywhere from half an hour to overnight. Be patient-- it may be a good time at this point to work on other parts of the process if your plans are settled enough.
3
Remove and tape your last. Once the last has solidified, it's time to take it out and get it ready. Cover your last with a colourless masking tape. That will keep it from being damaged as easily, and you'll be able to draw your designs directly on the last.

Outline your design on the last itself. Before you get to putting the pieces together, you'll probably find it helpful to give the last an outline of what you want the shoe to look like around it. While you shouldn't rely on it for concrete measurements, having an idea of what it will look like in three dimensions will help as you're figuring out where each stitch should go.