Each problem states a list of whole numbers and asks for the mean - add them up, divide by how many there are. It is the single most useful statistic to practise on its own before mixing it with median, mode and range, because it is the one with an actual procedure to get fast at rather than a value to spot.
Every list is built from its mean rather than checked afterwards, so the division always comes out even. "Find the mean of 4, 9, 6, 7, 4" answers to 6, not 6.4 - a fractional mean is a decimals question wearing a statistics one, and this worksheet does not print those.
The total shared out evenly across however many numbers there are. Add the list, then divide by its length.
Yes. "Average" in everyday speech almost always means the mean - add everything up and divide by the count.
The list on this worksheet is built starting from the mean, not drawn at random and checked. That guarantees the division divides exactly, so there is never a rounding decision to make.
Sixth grade (6.SP.A) is the standard introduction, usually alongside median, mode and range - our mixed mean, median and mode worksheet covers all four together.