There are four Shabbatot during the year when we read special additional portions in the Torah, two before Purim and two between Purim and Pesach.
Before Purim: Shekalim and Zachor
After Purim: Para and Hachodesh.
Parashat Shekalim is read on the Shabbat of the week when Rosh Hodesh Adar falls or on Shabbat Rosh Hodesh Adar. In a leap year of two Adar months, it is read before the second one. If Rosh Hodesh Adar falls on Shabbat, three sifrei Torah are taken out; one for the weekly portion, one for reading of Rosh Hodesh and the third for the reading of Parashat Shekalim.
The Haftara is read from Melachim II, Chapter11, which tells about King Yehoash of Judea commanding the Kohanim to consecrate all of the money brought to Beit Hamikdash for repairs and renovations of the Beit Hamikdash. This, indeed, is what was done.