As long as there are numerals, you can add the column. Put your cursor in the space where you want to see your sum and then click on the fx next to the address bar above the worksheet. Choose sum and follow the directions to have it do the addition for you.
Instead for deleting rows or columns, it may have been wiser to hide them. Highlight the rows you want to hide and then click on Format, then choose either row or column, and then Hide. You can always Unhide them later by following the same steps, but they're out of the way while you're doing your work and you won't have to do so much scrolling.
Hope that helps...
Saw your question about Format. You can format the numbers in a cell to monetary values, scientific, accounting, general, etc. With your cursor in a cell, click on Format at the top, then cell. You'll see several tabs there and you can play with each of them to set up your worksheet. The one entitled Number is where you will choose Currency and then look to the right to choose decimal placement, currency symbol and how to show negative values.
Hang in there...you'll catch on!