Is the statment true that you should at least have a net calorie of 1200 ? can someone please explain this, the benefit and how it works...

I was struggling to get them down to 1800 when I started. Now I am having trouble trying to reach 1000 net calories.

I think they're saying for your size and goals that you input here, it's suggesting you eat 1200 calories a day but also 'add back' to that any workout calories. So if you estimate you burned 300 on a run today, eat 1200+300=1500 today.

The problem with that is this site uses 1200 as a minimum so you won't really be racking up the deficits you 'signed up for' if you add back a bunch of exercise. You should still lose weight but it could be painfully slow. Eg, if MFP estimates your total burn for the day is 1800 and you said you want to lose 2 lbs/week, that would imply you should eat 1800-1000=800 calories/day. It won't recommend that low so it recommends 1200. So if you add back exercise, you're effectively only logging a 400 calorie deficit/day. Which is fine! But it'll take you a month to lose 3 lbs. so get comfy with logging. There's no reason you can't eat 1200 and burn 2200 (your 1800 plus a 400 calorie workout, for example), in order to shoot for the 1000 calorie per day deficit that is the recommended maximum by most authorities. You may not literally lose 2 lbs/week but it's a safe goal.