Yes, add all of your 4 lbs to the skimmer. Remember to pour very slowly, perhaps in batches over ten or more minutes, so there is never so much that it clogs the skimmer. After adding you need to not backwash/clean the filter for a week.
This time you want to add 2 ppm of chlorine, which for your pool is about six cups of bleach. You can do calculations like that one using the Pool Calculator. See the link in my signature. Add bleach by pouring slowly in front of a return jet while the pump is on.
This time you want to add 2 ppm of chlorine, which for your pool is about six cups of bleach. You can do calculations like that one using the Pool Calculator. See the link in my signature. Add bleach by pouring slowly in front of a return jet while the pump is on.