I can’t find the specific episode (probably because they eventually re-run everything on YouTube, so it’s hard to guess the seasons), but America’s Test Kitchen recently did a thorough spot on sourdough starters. The closest I can find is recipes on their website, which probably served as the “source material” for the aired segment. While I don’t have much personal experience, the “master plan” and “myths” articles both look solid and don’t require a subscription.

Making your own starter isn’t hard! You just need flour, water, and a food scale. (I started with the cheap scale from Walmart.) Feed your starter equal parts flour and water for about four days. Easiest amount is 113g. Keep it at room temperature so it can start fermenting. Once it’s bubbly, you can maintain it by keeping it in the fridge and feeding it once a week. I usually remove about half when I feed it and keep the discard for waffles.

Here’s an article that goes into more depth: https://www.thekitchn.com/sourdough-beginners-guide-23004397

You can make your own easy. I think King Arthur has some recipes, but the essence is: out flour and water in a jar. Add water and flour daily. Stir. Repeat. After like a week you’ll start getting some faction (bubbles). I made a levain with mine when it was your and feeding part back to the mother really amped it up.

There’s birthing fancy to these, just time. The yeast comes from natural yeast in the local air.

Most bakeries are throwing starter away daily. Just go and ask for it, many would be happy to share. You may also have luck with sourdough pizza places, that’s where I got mine when moving abroad.

In addition to buying a sourdough starter, you can also always try to cultivate some local wild yeast.

This page goes into it pretty well