Install Snow Leopard without CD

Okay, that's what we needed to know. Your Mac came with Snow Leopard, 10.6.6. I guarantee you cannot install the retail 10.6.3 version of SL on that Mac. The version you need were on gray DVDs that came with the Mac, and were supposed to stay with it. If the seller no longer has them, you'll have to get replacement disks from Apple.

Call Apple customer support and let them know you need to purchase replacement OS disks. They will ask for the Mac's serial number to make sure you get the correct ones. Typically, there are two disks. Pretty much the machine specific version of the OS on the first disk, and all of the bundled software such as Garageband and such on the other. Expect to pay about $45 for the two disks.

After you finally get the disks and install Snow Leopard, you'll be able to create an App Store account. Then download and install Yosemite.

First, there's no need at all to spend the money on Lion. You can go directly from Snow Leopard to Yosemite, assuming your Mac supports it.

Find the serial number on your Mac and enter it on this page. Please post a link to the resulting page that shows your exact model. This is so others can see what model you actually have, what OS it originally came with, and what is the newest OS it is capable of running.

Kurt, my two cents. Maybe you will disagree, but I wouldn't advise anyone to install Yos until at least one or two point updates, in order to get a version with at least some of the bugs removed. Seems like standard procedure with any newly released OS. Of course, it's possible it may go without a hitch, but I wouldn't bet the ranch on it. In addition to that, the OP should check compatibility of any apps with Yos.

That would normally be my position, too. I suggested it simply because that's the OP's goal. I'd strongly suggest installing Mavericks instead of Yosemite until it matures a bit. But we of course knows Mavericks is no longer available.

Might not remain supported through all of 2015, but the OP could still purchase a code for ML. Not terribly expensive, at $20, but not free either. Yearly release is really screwing things up. I have zero desire to run 10.10. Kept the installer for 10.9, so maybe I jump to that melting iceberg when ML is EOL.

They'll likely install Yosemite from a special version on their end that can be connected to your App Store account. That's important, otherwise you wouldn't be able to reinstall it.