Knitted cables: they look so complicated and yet all it involves is knitting your stitches out of order. Which for many requires a tool to hold your stitches on while you rearrange stitches. There are several styles: hooks (like a shepherd crook or candy cane), ones with a bump in the middle; or just ridged sticks. Then there are the magical cablers who don't use a tool at all but just pinch their stitches (but we don't recommend this when just starting!).
Some of these are wood, some plastic, some metal. Choose your poison. ;-)