From the second day of Pesach until Shavuot we count the 49 days of the Omer.
Counting is done after nightfall. Before counting a Bracha is said:
One counts both days and weeks, as the Torah says (Vayikra 23:15-16):
Today is the 8th day of the Omer which is 1 week and 1 day.
Source: Kitzur Shulchan Aruch 120:1
Wednesday, 23 Nissan 5777 - 8th day of the Omer