Almost but not quite - In my defence I was getting the kids ready for school.
=COUNTIFS(B2:B4,">01/01/2016",B2:B4,"<31/12/2018")
Where B2:B4 equals the range you want to count. The formula can go in any cell
Someone will respond in greater detail I'm sure as its thw cornerstone of NSC but it will be something like =COUNTIF(*highlight range* >01/,01/16, <31/12/18)