Everyone uses some sort a of medium to create their art. Here are a couple I find easiest to use:
1. Graphite pencils. They're almost always at your disposal and are great for black and white sketchs.
2. Sharpies. These I normally use for big projects like posters. They're great for adding color to just about anything. (Especially fun to sharpie your jeans)
3. Gel pens. For when I'm inking a sketch or free-drawing, gel pens are good for detailing.
4. Photoshop. It's great for adding minor details or completely changing the entire picture.