How can I create product mockups?

What I'd suggest, is to start with these courses:

If you are completely new to Blender:

https://cgcookie.com/courses/blender-3-basics-intro-to-blender

Otherwise you might jump in at:
https://cgcookie.com/courses/fundamentals-of-blender-materials-and-shading

Followed by:
https://cgcookie.com/courses/fundamentals-of-texturing-in-blender

And:
https://cgcookie.com/courses/fundamentals-of-digital-lighting-in-blender

And then you can begin modeling with:

https://cgcookie.com/courses/fundamentals-of-3d-mesh-modeling-in-blender

This last Course can be taken anywhere after the Blender3 Basics; it's pretty independant from the other three.

There will be a lot more to learn, but you will have a solid (and necessary) basis to work on.

For product shots your focus has to be in producing great compositions. So not only doing 3D, but having a great eye for photography and appealing arrangements. So I'd say you can also take courses on photography and how to make images pop with dynamic ranges and post-production.

When it comes to 3D is tricky, because one thing follows another. For example, you really need to know how to do great lighting for achieving great compositions. But your lighting will not work if you don't have great texturing and shading work on your model, and your texturing and shading depends on great UV layout and that depends on having a great model that subdivides correctly and if your model is not modeled correctly then all the errors on the model will probably come to light while doing lighting. So you see, you basically need to have a great model, that can UV correctly, so that you can texture it correctly so you can do some great shading so the your appealing lighting and compositions work correctly. So first thing's first, learn how to model efficiently and correctly. 

I like doing product shots and I love that it requires mastery of the whole pipeline and more. So don't be discouraged, all the contrary, it's awesome all the stuffs to look forward to.