I think there are two things to consider when we talk about graphic design. One is the use of the actual tools. Just like a carpenter, or plumber, you have to be somewhat comfortable using the tools of your chosen field. Instead of a hammer or a wrench, in the graphics and media field, we use macs and or pc's, and various software programs. You could have all the great ideas in the world, but that wont help you if you arent comfortable using tools to convert those ideas into something that others can see/hear/experience.
A program like Photoshop for example, can take years to master, but just about anyone with the desire can learn 4 or 5 basic functions and then build upon those skills. You could build some pretty impressive things with just a hammer, a saw, some wood and a bunch of nails. Then later on, you start to learn the use of power tools, and more advanced methods of construction. The same applies to graphics software.
As for the other part of graphic design, having the "eye"...well thats a little tougher. Some people say that you either have a creative eye, or you dont. It's sometimes tough to find out. The "design" part of graphic design means problem solving.
Your car has an interior that was "designed". Someone thought of what was needed, took into consideration all the things that they could and could not do, then began to "layout" the pieces in a way that would most benefit the user. In the case of a car, the user is the driver and passengers. In the case of graphics and media design, the user is the person that the images, sound, etc are meant for. The customer, the student, the course viewer...etc. these are the people that will "use" your graphic design.
If you want a free bit of education, you can do what the classical painters, sculptors, etc did. When they apprenticed with a Master, one of the things they had to do was to be able to re-create what their teacher had already done. In order to copy what someone else has done, you must learn HOW they did it, how they got to the end result. Find things that you see that you think are cool, things that you look at and say, "wow, i wish i had done that". Then copy it. Dont try to pass that copy off as your own work, but try to copy it just to see if you can! In that way youll force yourself to breakdown what the original artist did to get to the final piece. In this way, you may begin to see why they chose the images, colors, placement, type, etc. that they did. And then begin to take what you learn from them, and combine it with your own ideas to come up with something unique.
Hope this was somewhat helpful.