Remove the lump of blackish seeds from the cardamom
Grind them to a powder.
The skins are either discarded or mixed into tea leaves, to give a faint fragrance in the tea.
Though this is a wonderful way to use the skins, if one has a large quantity, then it is liable to go waste.
In my method, I grind the cardamom pods, skin and all to get cardamom powder. Roast the pods a bit, either on a warm griddly or in the microwave till just about crisp. Cool a bit, and then grind pods to get a fine powder. Sieve through a fine sieve. Transfer residual waste back to the grinder, add more pods and grind. Similarly finish with all cardamom. Store in a tight lidded clean sterile airtight jar.