How to count the number of rows with something in them?

COUNT will count how many have numbers, dates, booleans, and other numeric data. This excludes text. Numbers or other numeric data in cells formatted as text are also excluded (because they are text).

COUNTA will count how many have anything in them, including "white space" characters such as spaces and tabs and formulas that result in ""

COUNTIF(B,REGEX(".")) will count how many in column B have any character(s) in them, including "white space" characters such as spaces and tabs but excluding formulas that result in ""

COUNTIF(B,REGEX("[a-zA-Z]")) will count how many in column B contain at least one letter from the alphabet.

With REGEX you can be fairly specific about what you want to include. COUNTIFS can also narrow things down.

You can get a quick count without using formulas, by using a Pivot Table.

Click in data table and from the menu choose Organize > Create Pivot Table > On Current Sheet.

Drag fields in Pivot Option pane at the right, something like this:

SG