how to use Calc2LaTeX

That's fairly easy. Open any spreadsheet and select the rows/columns you want to appear in your table. Go to "Extras / Execute Macro / My Macros/Calc2Latex". Click on "Main" in the right side and "execute". It can take a few seconds before you will see the LaTeX dialogue which will allow you further settings.

(I hope the menu wording is similar in OpenOffice: I am using the German version of LibreOffice 4.1)