Chakra is energy extracted from cells that Ninjas need to be able to use Ninjutsu or Genjutsu. In order to use them correctly, the Ninja needs to mix their Chakra with their spiritual energy and then use special Hand Seals to activate the technique that they want to use.
A Ninja must train their spiritual energy through battles or specially targeted training in order to control large amounts of chakra when using techniques.
You may think Chakra is just a made-up thing, but it’s widely talked about in the real world. There are thousands of sites all about the Chakra energy. If you want to test your own Chakra, click here.