A Little advice

Some people eat their entire exercise back, some only eat some.

I myself try to only eat some and get my NET as close to what I want to have consumed for the day.

For example:
On days I work out: I will have my NET as close to 1200 + 50% of my cals burned during workout
On days I don't work out I will have my NET around 1200 (usually 1300 because I do move throughout the day lol)

Some people can give you the math behind all of it but this has worked for me for the past month and I'm down 10lbs.

It means that you can eat 1810+832 = 2642 calories with your workout and still be right on track to lose 2 pounds per week. If you go too far under your body could resist losing weight because of too much of a calorie deficit and it will think it's starving. If you go over, you won't lose weight as fast or will gain depending on how far over you go.

Basically, I try to stay 200 calories within my goal for the day, whether it's over or under that goal. Regardless of if you exercise or not, MFP will give you how many calories you can consume to be on track for your current weight loss goal. That number that shows as your available total calories (with or without exercise) for the day is your calculated amount to lose your 2 lbs per week. Keep in mind that even if you go over by 200 calories in a day, at a calculation of losing 2 lbs per week, you are still eating fewer calories than your body needs to stay the SAME weight. You just won't lose weight as quickly as if you're right on goal or slightly below it.

The way MFP works is you do NOT tell them about exercise until you do it.

So they created a deficit for you already, from the activity level you selected during setup. Hopefully you got that correct.

Because those non-exercise daily activities draw mainly from fat stores for their energy needs.

Exercise does not, hence the reason they are setup for you to eat back accurate estimates of exercise calories.
Otherwise known as feeding your workout.

Because the deficit is there whether you workout or not. It doesn't add more safe deficit if you don't feed the workout. It sabotages you effort if you don't.

As mentioned, if you don't have accurate estimate say from HRM or my only walking, then only eat back about 80% of them.

The secret is to net at or above your BMR. And increase your daily activities that don't need to be fed, as that is where the real weight loss will come from.

My instructor at the gym who put me onto this site told me to stick very close to the net amount of calories and I dont have to use any of the added ones from exercise and to save them as such if I go out to tea one night or get an unexpected invite, say to a barbecue. I havent lost any weight and she said the problem is Im too far under the net calories and my body is most likely storing fat. Also make sure you get enough protein. I am not seeing a change on the scale but not so worried as know Im losing inches. I will add you! The more support we can all get, the better!

I think you're a little confused here, what you are describing is eating your daily calorie allowance not your net.
Your net calories are your food minus exercise. So, if I eat 1800 and burn off 300, then my net = 1500. If MFP has set my daily calorie allowance at 1500 then I would be spot on for the day.

Does your trainer know that MFP doesn't take any exercise into consideration when it calculates your calorie goal? Most other calorie calculators ask about your activity level including exercise when they work out your daily goal, whereas MFP only adds extra cals for exercise if you actually do it, not just promise to do it!

I would agree that eating too far under your calorie goal isn't going to help you stay healthy for the long term and many people report that their weight loss is slow or stalls when they don't enough.

My suggestion (for what it's worth) - eat all the calories that MFP recommends, including those from exercise - I see no point in depriving myself unneccesarily. If I can eat those extra cals, give my body good nutrition to work with and still lose weight - why not?