Can I use Microsoft excel on iMac ? Does it cost for this app?

Here ya go.

http://www.microsoft.com/canada/mac/products

Yes you can. It is going to cost around 140 USD. However there are other products out there that are free:

http://www.libreoffice.org

http://www.openoffice.org

You can check those out.

Phil

You would have to purchase" Microsoft Office for Mac" to get the Apple OS X version of MS Excel.