You have many ways to add up figures in spreadsheets. The Quick Sum feature on the toolbar, for instance. Click below or to the right of a column or row of numbers, and click the Quick Sum icon.
Then the proposed total appears, and you can just press Enter or click the green checkmark icon if you want it.
However, sometimes things are a little more complicated? What if you had something like this, with groups of figures you want to subtotal? You'd want subtotals as well as a total. If you put in the subtotals with the Quick Sum feature, then you'd have to make sure that your Total figure included only the original cells, not the subtotal amounts, as well.
A situation like this is when you'd use the Subtotal feature.
Choose Data > Subtotals.
In the Subtotals window, in the first tab, select the columns you want to add up, and be sure that Sum is marked as shown.
If you don't want to add, but do averages or something, you can do that, as well. Select the function you want in the Use Function list.
Click the Options button and be sure that the Pre-Sort Area According to Groups option is unmarked. Marking it will reorganize the data, and not in a good way.
The subtotals will appear; here are the results with Sum as the function.
Look at the left-hand border of the spreadsheet; you'll see little + signs and brackets. Click each to determine which of the data you see; you can display everything for each group of data, or just the total.