Pencil drawing appeals to many aspiring artists because it's an inexpensive medium that can be extremely expressive. Drawings can range from quick sketches to full tonal artwork, and you probably have all the supplies you need to get started right now. Adding a few more supplies won't cost much, and you can find them at just about any store that sells stationary or school supplies.
You could produce a very nice sketch with a "#2" or "HB" pencil, and that's the hardness of most common pencils and the type you're most likely to find tucked away in a desk drawer. However, graphite pencils are made in several degrees of hardness, with "9B" at the soft end of the scale and "9H" at the hard end. I suggest that you purchase 2B, 4B, 2H, and 4H pencils to add to your collection. You'll be able to use these extra pencils to create a larger range of textures and shading than you could with just an HB pencil.
You could use the unlined paper you probably have around you right now for sketching, but you'll find that paper that's specifically labeled for drawing or sketching will have a texture that "holds on" to the graphite better than normal writing or printing paper does. You can usually find inexpensive drawing pads in the same store department that sells the drawing pencils. A few other handy items to pick up while you're shopping are a handheld pencil sharpener, a few different types of erasers, and a pencil box to store your supplies.
Most people want to draw realistically, and anyone can learn to draw that way with practice. Learning to draw what you see realistically requires that you see the subject in an objective way and that you move your pencil so that it mimics the shape or outline of the subject. Both of these skills can be improved by the use of a drawing "grid" and by regular practice.
A drawing grid breaks the subject into smaller and easier to draw parts, and it's easy to create a grid on top of a photograph. Print out a digital photo at the same size you'd like to draw it. Use a ruler and a soft pencil to divide the photo into halves and then quarters. Next, lightly draw a divided rectangle of the same size onto your drawing paper. Use a ruler to make sure the lines are straight and the squares are of the same size.
Now, mark on your drawing paper grid where the subject in the photo crosses each line of its grid, and then connect those marks as you draw the outline of the subject. Another way to use the grid is to concentrate on drawing just one rectangle of the photo grid at a time, eventually drawing the entire photo square-by-square. Lots of beginners, and some advanced artists, too, use this second method of grid drawing because subjects are more manageable when drawn in small "bites." Whichever method you use, erase the grid lines on your drawing when you're done and you'll have a lovely line drawing that you can leave as is or enhance with shading and texture.
Drawing is a very inexpensive and rewarding art form. Add a few items to your pencil box and make a commitment to learn how to draw. If you do, future generations might thank you for taking the time to express the beauty you see around you today.