I have never really had the ability to draw, but I've also never taken a formal drawing class. I am interested in graphic design and doing advertisements. Do you need strong drawing skills to major in graphic design?
I've never been a fan of storing socks either. But kidding aside, it is okay. Depending on the program you can certainly do advertising without being able to draw, that's what I do professionally. I didn't even study graphic design. You just have to realize your strengths and weaknesses and understand that it will limit the prospects. If a company wants a graphic designer that can do illustrations you shouldn't waste your time applying. If you excel at branding or concept then you'll end up focusing on that and it's limiting, but its not completely insurmountable. You could always spend some time while in graphic design school focusing on drawing in courses and your free time to strengthen your weaknesses. It always hard to get yourself to strengthen something you're not good at but its also very, very rewarding when you make it.
You dont need to have the ability to draw, what you need though is good visual imagination and sense of aesthetics.
Obviously you should be able to sketch so that you can visualize your ideas to customers and your bosses quickly, but sketches can be really loose so most likely you will do just fine.