How do I install 'Office: Mac 2011' without a disk drive?

Today I invested in a iMac.

I also brought with that the version of office for Mac. 'Office: mac 2011'.

The iMac I brought does not have a disk drive, I am meant to be isntalling this product with a 'Product Key' via internet. I've gone to the Office website and all but I am still confused.

I would like to install this product that I brought today, considering I spend a fair amount of money on it, opposed to buying it online.

Someone please help!

Kind regards, Renee and Rhea Wigley.