"Mi'shenichnas AdarMarbim B'simcha" – The Gemara teaches us "when Adar approaches, we increase our happiness" (Taanit 29a). Purim falls in the month of Adar--so great is the happiness of the holiday of Purim that it spreads out to the entire month of Adar. We begin our joy on Rosh Hodesh Adar, which falls this year on February 28-March 1.
This year, Ta'anit Esther (the Fast of Esther) falls on Monday, March 13 (13 Adar). Purim begins on Monday evening, March 13 (14 Adar) and continues to sundown on Tuesday, March 14. Shushan Purim, which is celebrated in Jerusalem and other ancient walled cities, is celebrated on the 15th of Adar (evening of March 14 and continuing to sundown on March 15).
There are four mitzvot specific to the holiday of Purim:
Reading the Megillah (Scroll of Esther)
Festivity and rejoicing (Seudat Purim -the Purim meal)
Sending food to friends (Mishloach Manot)
Giving gifts to the poor (Matanot La'evyonim)
And in case you forgot: Jewish law is restrictive when it comes to drinking alcohol, but Purim is an exception. "Chayav inish l'vesumi ad d'lo yada bein arur Haman l'baruch Mordechai'"(there is a mitzva on Purim to drink and become intoxicated until one cannot distinguish between the accursed Haman and the blessed Mordechai) (Megilla 7b). Chag Purim Sameach! Have a joyous holiday!