SUMIF(s)-COUNTIF(s)-AVERAGEIF(s)

Here is our example data

For SUMIF(s)/AVERAGEIF(s) we have
SUMIF(range, criterion, [sum_range])
SUMIFS(sum_range, criteria_range1, criterion1, [criteria_range2, …], [criterion2, …])

AVERAGEIF(criteria_range, criterion, [average_range])
AVERAGEIFS(average_range, criteria_range1, criterion1, [criteria_range2, …], [criterion2, …])

What these mean is - What range we're basing our criteria on, what criteria, what to SUM/AVERAGE.

For Example:

=SUMIF(A:A,"Apple",B:B)

Which would return 35.
or

=AVERAGEIF(A:A,"Apple",B:B)

which would return 11.6667.

Will SUM/AVERAGE B:B based on if A:A is Apple.

SUM/AVERAGEIFS works slightly different but similar concepts apply.

=SUMIFS(B:B,A:A,"Apple",B:B,">5")

Which would return 30.

=AVERAGEIFS(B:B,A:A,"Apple",B:B,">5")

Which would return 15.

Will SUM/AVERAGE based on if A:A is Apple and B:B is greater than 5.

COUNTIF(s) works slightly differently from the other two but the same concepts apply.

COUNTIF(range, criterion)

The thing here is there's no Sum/Average range so

=COUNTIF(A:A,"Apple")

Which would return 3

=COUNTIFS(A1:A4,"Apple",B1:B4,5)

Which would return 1

Will Count the number of occurrences the time Apple appears in A:A
and
Will Count the number of occurrences the time Apple appears in A:A and B:B is equal to 5