In all honesty the answer to this is one that is very hard to define. I have on several occasions thought that I had found the answer only to find out quite quickly afterwards that I did not actually know what I was talking about at all. Thats life I guess, thinking you know something only to discover that you don't. Graphic design, much like many things in life is no exception. It changes with the times like people do. Now the overall purpose of graphic design remains the same as it always has. To help advertise and communicate information in a visually stimulating way. That is not to say that it cannot be a vehicle for other things like tackling perceptions and changing the way people think about what they are doing and how they are interacting with the world around them because it does these things too.
What I want to talk about here though is less of a philisophical stand point on the nature of design and much more of a practicle guide to what you as a designer might get up to during your day. Mainly I aim to give you some helpful information that I had absolutely no clue about when I started my journey into the world of graphic design.
The profession is split up into subcategories that deal with different aspects of design (fairly obvious) and rightly so. Doctors may all be doctors but they all have their specialisms and the same applies for designers. If you are to become an expert in anything then the narrower the feild, the more accurate your expertise are likey to become. Don't take this as gospel I am sure someone will point out many things I have missed but the broad categories of graphic designers are as follows.
( This is largely made up of layout design for the web and is quite similar to that of brochure and magaizine design. The difference being however that the elements of interactivity in the web make the design process slightly more challenging as you have to figure out your customers behaviours as well as make the information palletable. Often web designers double as web developers (writing mark up language similar to what a programmer does) and have good technical knowledge to do with software and computers. Web pages themselves are just one part of web design though as there is a growing maret for e-marketing strategies, e-commerce, games, applications and so on.)
( Digital design is rather more aimed at interactivity than static design. It can involve anything up to and including web design, interface design, application design, and animation. This particular feild tends to be one of the more challenging ones as it is user oriented and involves a good understanding of semantics and usually requires a knowledge of both static and motion design as well as an understanding of programming laguages. There is more planning and testing involved in this feild than there is actual design as the emphasis is on how things work.)
Motion graphic designers,
( motion graphic designers bring static images to life. They tend to work in film, television, and animation, and take on a very similar role to that of the digital designer. (it is more likely that all of the above would work together on a project) they would do work such as idents, movie credits and dynamic web pages as an example.)
( There will always be work for the print designer despite what people might be saying due to the growing dependance on technolgy. Alot of the information we consume from day to day is in printed format. The menue at a restaurant, a business card, a bill from your phone company, the instruction maual that came with your new PC etc. Any where there is paper there is a print designer involved somewhere along the way.
( This requires virtually no explanation as they do precisely what there title suggests. Every single thing that you buy comes in packaging of some kind and therefore in our modern consumer society becoming a packaging designers could well be a great way to guaruntee yourself work (if you are good of course).
( The modern company has a real challenge on their hands when it comes to standing out from the crowd considering the fact that even your average joe can present themselves as a brand these days. Signage can quite literally capture an audience as well as inform on a location and help to navigate an area all at the same time. So the job entails some serious forethought. Then there are materials and costs to consider as well as environmental issues such as wether or not the sigange gives off light and disturbes the local wildlife and so on.)
( Although when we think of graphic design we tend to think of web design, interface design, and things like magazines what people forget is that typography does not just magically appear. Somebody dedicates there entire career to creatoing character formats, different lettering styles, entire font styles etc whilst all the while considering its legibility and tone as evry font has its own personality.)
So as you can see some of these categories blend over each other as the requirements for each job often require you to be multiskilled, but generally I think this is a fair representation of what kind of work is out there for people. Now under each one of these categories there is also a subset of roles within that. but these are the kinds of things that you will work out in your education and career for yourself so I wont go into that. What I hope you have gathered from this is that you wont be completely up the creek without a paddle if you find that any one of these genres doesnt actually suit you. There is always another one for you to try and the likelihood is your experience with the other may actually give you a head start in your new direction.
Like I said in my previous post for those of you who read it, you need to get stuck and be brave because your calling isnt going to come and bite you in the arse. Only time will tell (I am so full of cliche's for this I apologise) but knowing what is out there for you to try in the first place should be a big help. I didnt have a clue that half of these roles existed at all when I went to college and I think I would have benefitted greatly from it at the time. You probably already have a good idea wether you are more interested in motion or static or print or digital or 3d or flat etc. So trying out things in each of these will help you to realise where your strengths lie.