Q: in need of this software

Is the software  you are referring to Yosemite?

Is this a Mac that is second hand?  If so, what is the EXACT model/year?

Ciao.

On the back is the serial number.  Enter it here and post back the model and year information:

https://checkcoverage.apple.com/

Ciao.

You have to get your Apple ID associated with the MBP.  You do this by erasing the HDD and entering the original OSX.

Your MBP came with Leopard (10.5) and you should have been given the installation disk by the seller.  If not you can use this Snow Leopard Installation disk (which you will need anyway):

http://www.apple.com/shop/product/MC573Z/A/mac-os-x-106-snow-leopard

After you have erased the HDD and installed Snow Leopard, then you should run the Snow Leopard combo update:

https://support.apple.com/kb/dl1399?locale=en_US

That will then meet the requirements to create an App store account with your Apple ID and install newer operating systems.

Ciao.

Then you were in good hands and got it done correctly.  Good luck. 

Ciao.

Apple has removed both Mavericks and Yosemite from the App Store.

All you can download is El Capitan for free or buy Lion or Mountain Lion for $20 at the Apple Store.