Enter what you have held for a full lunar year. Mizan values gold and silver at today's prices, deducts debts due now, and compares the total with the nisab. Leave anything you don't have blank. Nothing you enter is stored.
Zakat is 2.5% of zakatable wealth held for a full lunar year at or above the nisab. Many scholars and charities use the silver nisab because it is lower and so reaches more people; others use gold. Your home, car and personal belongings are not included, and on the majority view neither is everyday jewellery. For your own situation, ask a scholar or a zakat organisation you trust.
Developers: the same calculation is free at /api/v1/zakat.