How does Anymod handle data edited from the CMS interface vs edits made directly to the source?
Typically people maintain their source code as usual and then add Anymod wherever they want the content of the page to be easily editable. So for example, you might have a setup that works great, but you want some of the images or text to be easily changeable. You can add Anymod to just those pieces and keep everything else however you like it.
Okay, so assume I have a mod that has text associated with it. IN my code I insert the mod and tell Anymod to render it when the page loads. If I wanted to change that text, the only way I could do so would be through the CMS interface correct?
Yes, either by visiting your own website or in the Anymod dashboard.
If you visit your own website to edit the content, how do you restrict access so external visitors cannot edit the content?
If you are logged into Anymod, it will automatically know. You can also create a link that redirects to your website, and you can save that link or share it with your team.
By default the links let you make drafts (but not publish). You can add a password to the link to be able to publish.
So you or your team can have a workflow where you never even have to log into Anymod to make edits 
Ok thank you, I was trying to under how the CMS functioned. But thank you for answering my questions