Is it easier to do math in excel, or just use a calculator?

I have a lot of sums I have to add up, and was advised by my boss that it would be best to use Excel to do it; however, i'm having a hard time figuring out how to add all these numbers together using excel. I tried the tutorial and it's not really giving much info. Which is most convenient to use, Excel, or a calculator? And if it's Excel, then how do you get it to do the math? Any help appreciated thanks.