Feeding the Starter
Equal parts starter, water, bread flour - So if your recipe calls for 100g of fed starter…(read the recipe that you plan on making and take what the active starter amount is and divide by 3, to get the amount of equal parts of starter, water, flour)
40 g starter
40 g water
40 g Bread flour (high gluten flour) the higher the protein % the better!(see my list of flours)
Start by placing a 4c wide mouth glass jar on your scale, zero out, Add 40 g starter, zero out, Add 40 g water, zero out, mix till milky white and mostly dissolved, Add 40 g Bread flour (or your favorite high protein flour)
Mix in the glass jar, should be a saggy wet clumpy batter like consistency
Scrape down the sides, so you can clearly see where your line of starter,  starts at. Mark with masking tape/ or rubber band. Loosely cover with jar lid or plastic wrap (do not make air tight, you want it to be able to breath so when it starts becoming active the air is able to escape. But covered well enough that bugs or dust can’t get in.
Let sit on the counter for a bout 6 hours give or take depending on how warm your kitchen is. 
(Do not leave in direct sunlight and do not let it get too warm) *never let anything fermented (traditional yeast, sourdough, yogurts, kombucha, Keifer, etc) go above 95 degrees. Ideal for sourdough temperatures 70-85 degrees. My kitchen fluctuates between 70-78 I feel closer to 72-76 degrees is my sweet spot and I have perfect bakes proofing at that temperature. You just made 120 g of active starter, 100 g for your recipe, and 20 g to store in the fridge to add back to your mother.
Very important you mark your starting point… you want to use the starter once it doubles in height… but the trick is to catch it at its highest point before it starts to drop… once it drops it starts to loose its activeness. You want to use when it’s at its most active state. (A trick if you are unsure or if you forgot to mark, you can fill a glass of water and drop about a table spoon of starter in the water if it floats then it’s active… if it sinks its over its peak and lost its activeness.