|There are a number of ways to write a formula using the SUM function.|
For a simplistic explanation, look up SUM in the Excel Help files and review the info, especially the examples at the bottom.
Then, if Add Numbers doesn't appear as choice when you search for Sum in Help, search for Add Numbers for lots of detailed information.
And please, please...don't included multiple "lol's" in your posts.
My error...I didn't notice that you were using Calc.
In any case, as Mike says below, SUM is the function you need and reading the Help files is usually the best place to start.