The Hebrew calendar is a combination of solar and lunar. Instead of a "leap day" every 4 years (as the Gregorian calendar has), the Hebrew calendar has a "leap month" every few years during a 19-year cycle (7 times in that 19-year cycle to be exact) that helps to keep the lunar and solar cycles in sync. The month of Adar becomes Adar I and a "leap month" of Adar II is added. That is the pattern for this year.
The Hebcal Jewish Calendar website says this:
Purim Katan is a rare guest that deserves special attention. In the 19-year cycle of regular and leap years we have nineteen Purims, but only seven Purim Katans. We must truly utilize it for special activities.
There’s a strong connection between Purim and Purim Katan. The Mishnah teaches: “There is no difference between the first Adar and the second Adar, but the reading of the Megillah and the distribution of gifts to the poor.” (Megillah 6b)
Otherwise, both Purims are the same, with Purim Katan being first!
The theme of Purim is the victory of the Jewish people over their enemies. A running gag about Jewish holidays is this:
They tried to kill us. We survived. Let's eat!
While there are treats to be had as part of Purim, the greater blessing (of both the "little Purim" and the big one) is that we should make them days of feasting and rejoicing and sending portions of food to one another and gifts to the poor. (Esther 9:22)