This is regarding my Avacado tree/plant! I am confused as to what i should do with it in the next step! help!?

A few months ago i decided i would put a avacado seed into my cactus pot and see if it would grow. I put it in the proper way and then I forgot all about it! I never water my cactus and so the avacado never got watered. Today i looked and there was a tall shoot comming up! It was my avacado tree! I was very excited. but now i need to transplant it. my question is. do i need to place the root in water, since the root seems to be just one long stick like thing. or should i just stick it in potting soil and water really well to get it going! I am so excited, but i have already take the avacado out of my cactus so i have it just sitting on my counter.. i need HELP IMMEDIATLY! but i am so STOKED!!!