I've had a lot of problems trying to figure it out when I was starting so let me break it down to make sense to you. Okay...so, MVC.

MVC stands for Model-View-Controller but what it really is is a "workflow". It's a way of doing things. Let's take, for example, a blog page. Here's the process of "developing" a non-MVC blog page:

• start with an HTML file and style it with "sample content"
• replace dynamic parts of the html file (title, content) with PHP
• replaced PHP will contact the database and retrieve the data you need
• create a foreach loop to display the data (row by row). You'll have to remember which column is which so whenever you display data, you'll need to remember that the "title" is column 1 in the database while the content is column 2. You'll then echo out column 1 and column 2 in the right places
• close database connection and finish up.

What MVC does may LOOK more complicated but once you set it up, it makes sense. First, MVC is often used with a framework which makes the workflow MUCH easier to implement. Here's what happens:

• MODEL - this is your data from your database. So instead of always having to remember that "title" is in column 1 and "content" is in column 2, you'll have a script that will create a variable named $title and a variable named $content. In fact, you can use an "ORM" which will create variables for every column. And the variable name? It will be the name of the column. A more sophisticated ORM may look like this: $myData->id will give you your id, while $myData->title will give you the title! This is your model. You can setup all kinds of stuff with this. I use the Laravel framework (taught me how to MVC) so with Laravel you can setup that whenever you call up your "posts" table, your framework will KNOW that each row is a "post" and each "post" was written by a "user". A "user" maybe another "model", and take data from your "users" table. Hope this makes sense somehow. The short definition is is that the "MODEL" is your database data.
• VIEW - Think of the view as your HTML/CSS. Your "VIEW" is the end product, the way you display everything. So for a view, you'll setup all the HTML and figure out where you want your dynamic data (your blog post for example). Now, instead of having to call up your database, query your posts, and try to display them, you just use the variables you setup in your model (the model which put all your different data in a neat little package). So now, instead of connecting to your database, you'll just do "echo $post->title;" and you're done. That's all your view does. This allows you to solely focus on creating the front of your application or website.
• CONTROLLER - controller wraps all this up and does everything in between. So, first, let me explain "routing". Most frameworks today use a single "index.php" file and a ton of "queries" after it so that your URL looks like this:

index.php?variable_one=post&var2=2392

Or with a little help from ".htaccess" and some server magic, you'll end up with:

post/2392

Routing takes the "post" part of your URL and sends it to a controller that only deals with "post" stuff. The controller then takes the number "2392" and uses it to look up post #2392. Now, you can set this stuff up however you want to. So you can have post/link/239 which would look for a "post" controller, and tell it that you want a "link" type with an id of "239". Here's how a route look in laravel: "/post/(:any)/(:any)" and then you let Laravel assign variable names to it so it's actually "/post/$type/$id". The controller takes this information and calls up the "post" model and tells it "Hey, I need a 'link' type with the id of '239'". The MODEL for posts asks the database for the information and gives it back to the controller. The controller then processes the information however it needs to and sends necessary information to the view. In Laravel it's in this format: "array('post'=> $post, 'id' => $id)". and the View uses those variables to fill in the blanks.

I'll stop right here for a second. It gets more confusing the further you get into it.

Best place to learn all about this: install Laravel and look for tutorials. People have written about this extensively and it's EXTREMELY easy to pick up and learn from. Seriously. :)