Yes you can cook chicken from frozen as long as you cook the chicken longer.
It's best to cook chicken when thawed out so that the chicken does cook evenly especially if you're grilling the chicken or cooking the chicken in a skillet.
However deep frying the chicken or baking the chicken from frozen is okay and it will cook just fine but just takes longer.
I've always just put frozen chicken into the oven or into the deep fryer and cooked it without thawing it.
However if you do want to thaw the chicken out which you should do before grilling the chicken then remove the frozen chicken from the freezer and allow the chicken to thaw in the refrigerator for 24 hours.
Never leave the chicken out at room temperature to thaw because bacteria can grow on it.