The basics of sketching are easy and fun. Basically, you need some paper and you need a drawing material. This time, I'm going to use drawing pencils. Drawing pencils come in different shades. You have B as in boy, pencils, and you have H as in Harry, pencils. The Hs are much harder and lighter toned. The Bs are much softer and can be much darker.
When it comes to sketching, the most important thing is to really have your tools ready, and to experiment. Sketching and creating art is all about creativity; it's all about tapping into your own sense of creativity and expressing yourself. If I'm going to explore sketching, the most important thing, really, is just to see what does this tool do? For example, how dark of a line can I make pressing really hard? If I barely press, how soft of a line can I make? Perhaps I'll pick up another pencil and do the same thing. Immediately, I see that one pencil is much darker than the other. On the contrary, this pencil is going to draw a much finer line. You want to explore what types of lines you can make. Sketching is all about self-expression through creating a variety of lines.
My suggestion to you would be to draw a lot of different lines on a piece of sketch paper. Perhaps draw circles, draw dashes, perhaps even think of words, and draw the types of lines that come to your imagination. For example, if I say 'exciting', what types of lines might you draw? If I say 'peaceful', what type of line might that be? If I say 'sleepy', what type of line comes to your imagination? If I say the word 'loud', what kind of mark or line comes out automatically?
As you explore your sketching, I recommend this type of exercise; think of adjectives or experiences that you've had and come up with very quick symbols. You'll find that you can create a wide variety of sketch marks and sketch lines, and this will be a perfect introduction to exploring the basics of sketching.