The ground chicken is sold in 1lb packages in the meat department by the chicken and turkey. You cook it in a skillet, just as you would ground beef and then add a package of taco seasoning and the water called for on the seasoning package. Then make your tacos as desired.
I have heard that ground turkey tastes the same as ground chicken and is good in tacos too, but I have not tried it. Ground turkey is supposed to be healthier than the chicken also.