Tomatillos are notoriously difficult to grow. Tiny seeds have low germination rates and tomatillos need to grow in groups in order to cross pollinate and produce fruit.
Wait until all danger of frosts have passed before sowing outside, or start seeds indoors 8 weeks before the last frost date. When transplanting, you can bury half of the plant like you would a tomato. Keep the plants about 3’ apart. When picking a spot for growing, pick an area with acidic soil and full sun. You will need stakes, a cage or a trellis for the tomatillos to lean on. Make sure that all of the fruit remains off of the ground or you can get slugs/snails attacking your plants. Tomatillos can also be grown in large pots (as long as you have multiple plants in the same area). The plants will grow all summer and will die in the fall with the first frost.
After flowering, the papery husk appears and then the fruit fills in. Harvest when the fruit is green and has filled out the husk. They can ripen further and split the husk, which will then cause them to change their final color, but the flavor changes. Tomatillos can be stored in their husks in a paper bag in the fridge, or by removing the husk and freezing.