Excel Problem: Find out the number of cells in a specific area

Solution: ROWS(range)*COLUMNS(range)

Functions:
ROWS(array)
Returns the number of rows in a reference or array

COLUMNS(array)
Returns the number of columns in a reference or array

Excel Problem: Find out the number of not empty cells in a specific area

Solution: COUNTA(range)

Functions:
COUNTA(value1;[value2];...)
Counts the number of cells in a range that are not empty

Excel Problem: Find out the number of empty cells in a specific area

Solution: COUNTBLANK(range)

Functions:
COUNTBLANK(range)
Counts the number of empty cells in a specified range of cells

Excel Problem: Find out the number of text cells in a specific area

Solution: {=SUM(IF(ISTEXT(range);1))}

Functions:
SUM(number1;[number2];...)
Adds all the numbers in a range of cells

IF(logical_test;[value_if:true];[value_if_false])
Checks whether a condition is met, and returns one value if TRUE, and another value if FALSE

ISTEXT(value)
Checks whether a value is text, and returns TRUE or FALSE