IT:AD:Google Apps:HowTo:Configure Outgoing Email
Process
I don't have screen grabs for this, and not willing to undo it all to get them, but somewhere around here, Google Apps will ask you to verify ownership of your DNS records and give you an instructions to create an CNAME with it. By finding it, it proves you are authorized to update the DNS records for your domain.
Next, it will ask you to make CNAME alias pointing back to their website. They'll take the request from there.
As for the MX records… I also can't remember how these were set up, but I'm pretty sure they just tell you what the MX records you should be using are and you enter them in your DNS. As follows:
That's all there is to it.