There are 2 types of alms both of which are mandatory if the person is not in financial strains. One that's due for money and valuables (i.e. gold and silver) when a full year has passed on their possession/accumulation (please take the time to lookup more information with regards to this type of zakah). The other is the Fitr Alms that's due on the day of Eid before the Eid prayer and not after.
Collection boxes are available inside the mosque, calculate your Zakat when you paid last time and drop the amount.
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