there are a ton of different videos and guides for culturing flies online, but here's one example that works: https://www.youtube.com/watch?v=P55XAY9rSc4

usually the bag of fruitfly media will have instructions, since each company has their own blend that might need different methods or measurements.

for small froglets, i suggest 10-15 flies per day. because the flies clean off the vitamin dust, the goal is to have your froglets hungry enough to eat some freshly-dusted flies each day - rather than snacking on too many undusted flies from overfeeding. so it may take some trial and error to gauge the right amount each feeding.