You can install the MS Office Application using the Discs you have by following the steps below:
http://office.microsoft.com/en-us/help/install-or-remove-individual-office-programs-and-components-HA001234067.aspx?CTT=5&origin=HA010173340
If you do not have the MS Office Discs, then you can download and install the Trail version of MS Office in your Computer from the following link:
http://office.microsoft.com/en-us/try/try-office-2010-FX101868838.aspx?WT.mc_id=MSCOM_bnr_enus_try
You can click on "Try it Now" for "
Office Professional 2010" to download the Trail version.
The Trail version once expired, you may have to buy a license from Microsoft to continue using MS Office.