The day we acknowledge, that Hashem saved us from the evil decree of Haman. It is customary, to dress up. It is Halachikly correct to give "Mishloach Manot"- At least, one ready drink, and one ready food. It is also Halchikly correct to give "Matanot Le'Evyonim"-Money to the poor. It is Halichikly correct to have a "Purim Seudah"- A meal, where one should finish half hour before Mincha. According to Kabbalah, one should have the Seudah after Davening in the morning. It is customary to get a little drunk(Not to much).