Beginner Question About Exercise Calories

Hello! I am new to exercising and dieting but have a question about tracking exercise. If I complete an exercise, myfitnesspal will add the calories burned to by daily food allowance. But I believe I would also be burning calories just sitting down. So let's say I go for a walk and log 60 min leisurely walk, it credits me with 400 calories burnt. But had I just sat around maybe I would have also burnt 200 calories in that hour. So, can I really eat an extra 400 calories and meet my goal, or should I adjust for the calories that I would have burnt doing nothing? Thanks!