Purim, pronounced "Pour-ree-im", is the name of the celebration. Purim, in Hebrew, means "casting lots". In the story, the evil Haman cast lots to determine the day on which "Israel" would be destroyed. The same abomination will happen at the end times, to destroy all of those who keep the commandments of God and hold to the testimony of Jesus. (Rev. 12:17)
[Note: as for me, this verse should awaken all "believers" who still think Torah has been done away with! Jews and Christians alike should wonder why those who follow the commandments of God AND hold to the testimony of Yeshua are worthy of the persecution. You know - the Remnant that follows the Narrow Path! Folks, it's time we understand and actually believe what the Bible says, not man!]
Here are two calendars showing when to celebrate. One is from 119 Ministries and the other is from Michael Rood. The calendar "argument" is a huge subject best left to Yehovah to sort out - and He will. : )
Here is a good reference for the celebration of Purim. As always, be sure to filter out any Rabbinical rulings, while keeping in mind - all tradition is not bad, as long as it does not add to or subtract from His Word! Also, you will discover that each person or religious group has their own interpretation of the events in the book of Esther, so don't be shocked if you come across a myriad of eschatological "flavors" when you conduct your research.
So, I recommend you sit down, read Esther, study it, and decide how you wish to celebrate. Purim is not one of Yehovah's instructed Feasts or Holidays, but is a tradition.
BTW, many scholars say Yeshua was on His way to Jerusalem to celebrate Purim when He first stopped at Bethany and raised His friend Lazarus from the dead. Coincidence? Not likely, in light of the story of Queen Esther! : )