Welcome to MCC !
MCC stands for My Cover Creator - a graphic editor tool to design your social media page header (Facebook for now), but soon for Google+, Twitter, and whatever social networks to come in near future.
Some technical stuff.
For short, here are some main features and goals of MCC.
MCC (this version) is intended to help improve your main Facebook cover design, give a boost, a unique look and feel for your presence on social networks.
Basically you can design your own cover using few tools, your resources (photos, designs), your annotations, all blended with your imagination and creativity.
There are companies that offers such services like this for money, but here you can get all for free, this will be your creation, your skills, and finally your satisfaction. :-)
So, MCC is a graphic editor using latest features of HTML5, CSS, JAVASCRIPT, WebGL capabilities of modern browsers.
For short, to understand how it works you must know that:
Using MCC.
Using MCC is free. However, please consider this:
Finally, some words of wisdom.
For the sake of performance don't load huge images into editor; it's a waste of time since the image is redimensioned to fit the 851px Facebook cover width dimension. If your image has a portrait layout, or height of image is greater than 315px, you should move image up and down, and choose the most reprezentative part of it, and crop accordinglly using 'crop image to visible' feature from LAYER BOX.
Just click on this icon    from LAYER BOX. It's highly recommandable to do so, because this way you'll avoid usless rendering on invisible parts of image when apply effects, shadows, converts etc.
And usless renderings that take time and slowdown the workflow process.
As a remainder, some operations, like blending or WebGL effects, make this cropping to visible operation by default, bringing image dimensions to default values of Facebook cover. (851x315) pixels.
Premium effects (recte WebGL effects) works only for latest versions of Chrome, Firefox, Safari(not tested), and IE (ver.11 and greater). You should know this, if you decided to be a premium user.
In order to run smoothly MCC needs a decent Internet connection, due mainly to graphic operations that are resolved and logged on server. If you encounter some network error message, try set from LAYER BOX -> Arrange -> Network speed adjust settings -> Slow.
This will not increase MCC speed, but in some cases you'll get rid of this problem.
And last, but not the least, update your browser. The lowest entry level browser that MCC can function, with is IE 9. Sorry for old XP IE 8 systems, but that's life. This is due mainly to the new HTML 5 features requested by MCC to work.
There is also a version for mobile. Unfortunately the core of MCC capabilities is missing, simply because there were too many controls on such small screen, but we are working on it :-).

So, happy cover editing, and have fun !