The Wiki on the tag mvc
can be a good starting point.
MVC is a theoretical model, a design standard. There is this Sitepoint link that can serve as a tutorial for your case, in PHP. It’s a little long, so I don’t know if it’s worth posting an entire answer about.
To improve your knowledge, I think it is also worth going to a better finished solution in a Framework, like Codeigniter. Standards and good practices already exist in the Framework and this one in particular requires you to write several manual steps.
Another great framework is the Laravel.
Both have several questions answered here at Sopt.
About their difficulty in designing solutions, the way is to study, make examples, learn a three Frameworks, point out the differences about how they solve problems, and ask here. Bring your questions in a more specific way by putting code ready and asking for more code. There is not much secret.
I would recommend Kohana as a starting point for teaching purposes.
– Papa Charlie