The primary mitzvot of Purim include: Hearing the Megila both evening & morning; Matanot Levyonim (giving at least 1 gift to at least 2 poor people); Mishloach Manot (giving at least 2 ready-to-eat items to at least 1 friend); Seudat Purim, the festive Purim meal eaten on Purim afternoon. On erev Purim it is customary to donate Machatzit HaShekel, the 1/2-shekel, giving 3 of the fixed coin of our own time & place (1/2 shekel in Israel, ½ $ in the USA, etc.). Why 3? Because the pasuk uses the word "Truma - offering," 3 times. "Al Ha-Nisim" is added to the Amida & benching; the Purim morning layning is the years’ shortest (& satisfies the command to "remember Amalek" if you missed Zachor). The Gemara says one should drink on Purim so he is unable to distinguish between "Cursed Haman" & "Blessed Mordechai." But many authorities suspend this Minhag if drinking leads to improper behavior or drunk driving, is a danger to health or impairs our ability to daven with proper kavana.