What is the fast way to add up this column of numbers after clicking in the cell below the numbers?

You can click the AutoSum button then you can just press enter. Excel is known to be one of the best programs that you can use when you are making tables or when you are trying to make some important computations.

It will take time before you understand all of the needed formulas so that you can make vital computations but once you know everything, this will not be a concern for you anymore. You will know what to do whether you need to find the average, the sum, and so much more of the data that you have placed in the various cells of the file.