Congratulations! You are the owner of an ultra-local sourdough starter. I encourage you to name yours. This way, you are more inclined to feel guilt when you neglect it. ;)  Ours is Shiva.

To start your culture, crumble your flakes into 100g warm water, add 100g of flour and mix. (That’s about ½ cup room temperature water and about ¾ cup flour.) Place in a warm spot for 8-12 hours. Then, discard most of your mixture, leaving about 25g and repeat the feeding with 100g water and 100g flour. You will likely need to repeat this step 2-3 times before you begin to see activity. At this stage, rely on times rather than visible activity.

The container you use is not terribly important, but a glass jar or see-through plastic container is helpful so you can track its progress from the outside.

Once the starter is revived and ready, it should look like the photo below: bubbly, aerated, and doming slightly. It will have risen to double its size. (Photo courtesy of 'Modernist Bread' 2017. "Mature" is your goal.)

A reliable way to test if your starter is ready is the float test. Fill a glass with water, drop in a walnut-size piece of the starter and if it floats or drops to the bottom but rises slowly, it is ready. If it sinks but it has been less than 6 hours, keep waiting. If it sinks and it has been more than 10 or 12 hours, it has gone too far; start over.

To keep your starter alive and well, you’ll need to feed it 1-2 times a week. Keep it stored in your refrigerator until it’s time for feeding, at which point repeat the 25g active starter + 100g water + 100g flour. Leave it out at room temperature to get active again, then return to the refrigerator.

If you don’t plan to bake regularly, simply work flour into your active starter—no water this time—and rub together until the mixture turns to dry crumbles. Store that in the fridge for up to 3 months; it will take 4-5 feedings for it to be healthy and active again.