Give Mahatzit Hashekel - Half a Shekel: מחצית השקל
The source of this mitzvah is the Torah, Parashat Teruma, where every man over 20 years of age gave a half shekel (silver coin) as a donation and to count the population. Later on at the time of the Beit Hamikdash - the Holy Temple, the money was used to purchase cattle for the communal sacrifices which were offered daily as well as the additional sacrifices offered on Shabbat and holidays.

Today: It is customary to give the equivalent of 10 grams of pure silver as the half shekel. Today that comes to about $8.5 per person 13 yrs+.

When? Most people will give it on Ta'anit Esther - the fast of Esther, which falls on Thursday, February 25, 2021 BEFORE Arvit, OR any time during Purim.