CountIf
The Count function returns the number of rows in a table or group for which all given conditions are true.
Syntax
CountIf(condition 1, condition 2+...)
Function arguments:

condition 1 (required) The condition to test. If the condition is True, then the row will be counted.
You can use operators in conditions.
 condition 2+ (optional) Additional conditions to test. If multiple conditions are given, they must all be True in order to be counted.
Example
CountIf([Age] > 65)
 Count rows where Age is greater than 65.
CountIf([Age] > 65, [State] = ”Ohio”)
 Count rows where Age is greater than 65 and State indicated is Ohio.