Taylor uses MAC Paint Pots and MAC liquid eyeliner to draw on her 13. The right colour of the MAC paint pots has been discontinued (although it may still be available in your nearest store, go check it out) but the liquid eyeliner she uses is still available. Don't just limit yourself to MAC products, almost any cream eyeshadow and liquid eyeliner will create the same effect, like this cream eyeshadow from Sephora.
There are many ways to draw on your thirteen (over time people have suggested the eyeshadow/eyeliner method, using sharpies, using nail polish and many others) but I believe that Taylor's original method of eyeshadow/eyeliner is safest for your skin and looks closest to the original.
1. While looking at the style of Taylor's 13, draw a thirteen on your hand using cream eyeshadow (I find it works best by drawing the outline out in blue, then colouring it in, working from the outside to the inside). Although you can apply it with your fingers, I'd recommend using a make-up brush (like a lip brush) to get the best coverage.
2. To draw the outline, you can using liquid eyeliner in black to achieve the same effect. Some people prefer to do this using a black sharpie, but the pen can be difficult to remove from your hand and can irritate sensitive skin, so I wouldn't recommend it.
3. Allow the eyeshadow and eyeliner to dry out, then spritz with hairspray to ensure it doesn't smug.
Taylor sometimes puts little rhinestones on the 13, which you can get from your local craft store (or use ones that sometimes come in nail sets). The safest way the apply them is using a skin-safe glue like eyelash glue, then apply a fresh spritz of hairspray.
