Working out adding calories to my calorie goal??

That confused me as well! lol I If I just did a workout to burn lets say 400 calories,,if I eat 400 additional then doesn't that just pretty much wipe out the exercise I just did?

Yes, you should eat your extra calories. Think of food as fuel for your body. Providing you are eating healthy (most of the time), then you need these healthy/good foods to recover from the workouts that gained you the "extra calories".

There are two main schools of thought on the matter. The MFP school calculates your sedentary TDEE (Total Daily Energy Expenditure) and then has you track your exercise and add calories to your day based on your caloric outputs. The standard TDEE method is to calculate your daily calories including normal exercise routine and simply eat above (for gaining) or below (for losing) every day without variance. 20% above or below is the typically agreed upon number for efficiency and sustainability with larger differentials possible for short times, but not suggested.
It is generally agreed that MFP overestimates caloric burn for activities, so if it adds 300 calories to your day, most would say to only eat back half of those.

Eat back some or all the cals.

Let's say that MFP has a 1 lb week weight loss goal set. You should eat (NET) 1400 calories/day to lose 1 lb week. You workout and burn an additional 400 calories more than what MFP thought you'd get based on what you entered as your activity level. Now, you eat 1400 calories - minus the 400 EXTRA you burned and you now have a net of 1000 calories. Now you will lose say 1.5 lbs/week - when you wanted to lose only 1. Eat back the 400 (or a little less - since MFP may overestimate calories burned) and you'll net 1400 as you wanted. Don't eat back the 400 and you've netted 1000 cals.