You might not need to tell them you are a Witch at all my dear, the thing about this term is it's often very misunderstood by the community outside the occult. You see a Witch can be a Witch without practicing witchcraft. There are many many different paths, faiths and cultures that come within what one would call witchcraft. So you could say for example that you've started worshiping Odin or Freya, or you've started adopting certain shamanic practices etc.
I would stay warry of telling them. The main code amongst wiccans: to know, to dare, to keep silent. People have been killed, exiled and burned alive for witchcraft. It's best not tempt unless you can be sure. Once the black cats out of the bag it can't be put back.
I think as you grow you will feel more comfortable :) when I started it was an interest I always had .I was brought up as a catholic but my spirituality did not feel satisfied to just stick to what I had been brought up to believe, I was always interested in the senses and the energies and I needed to satisfy my own spiritual awareness which I felt I needed to learn for myself ! To be honest it was personal and I did not go shouting it out from the rooftops but as I adjusted to my way I never felt I had to explain or hide it !!
Hope this helps somehow !