Showing list of nodes related to logged in user using views I have some content of content-type "mockup". The "mockup" content-type has a field that references a user (so when I create a mockup, I can select a user for it to "belong" to).

For some reason, I can't figure out how to use views to get all "mockups" that belong to the logged in user. I thought it would be in "contextual" but I don't see anything like that.

I don't want anyone to be able to view the node unless they are the "related user", is this a "views" thing or a "permissions" thing?
I'm not sure about the details of your use case, but it might be easier to set the author of the node to the user rather than setting up a field with a reference.

You can set the author manually if you have administrator permissions.  You could also use the Rules module (via the "Set a data value" action) to do so automatically.

If you use this method, you can simply set the permissions for "View own content of type ABC" and "View all content of type ABC" that are provided by default to limit access.

For your view, you can add a "Contextual filter" of "Author".