Under my allowed calories???

you should always log your food and exercise. The app will adjust for the calories you burn during exercise. If you fall short of your calorie goal you are in danger of not getting enough nutrition to support your body. Also, I've noticed if I am less than 1200 calories and I log it the app gives a warning about starvation mode. Starvation mode is when your body stores whatever it can and slows down your metabolism. Its best to be within 100 calories of your daily goal.

It has been my experience that 'some' under my goal calories is generally okay, but I do watch that carefully. You probably know that too little calories causes your body's 'furnace' to burn out (store energy as fat). If you set your weight loss goal wisely (1/2 - 2 lbs per week), then you should aim for your target calories to maintain a healthy, long-lasting weight loss. Your calorie target is figured with your exercise goal in mind. If you are meeting that goal, no need to take in less/more calories. If you are far exceeding your exercise goal, you may need more fuel (calories) to keep your body's blood-sugar stabilized, thus burning calories. As a rule of thumb, a 3000 calorie deficit (from your body's at-rest metabolic need) will result in loss of one pound. This is the rule this program uses to determine your target calorie range. Hope this helps and doesn't add to your confusion.

I would love to find a way to also track sodium, etc.

I was wondering this also!

I find sometimes I am under my calories by 200-300, but I am full because I have eaten big nutritious meals.

Should I eat for the point of eating? or can I "save"these and have an indulgence on the weekend?

There are quite a few people who save the calories and indulge on the weekends. In my own opinion, if your not hungry, you shouldn't force yourself to eat. I don't even worry about if i'm under too low, I focus on if I'm hungry or not. If I am, I eat more, if not, then I don't.

I think she mistyped 3000, I can't remember the exat number for deficit but I know a 2 lb per week loss requires a 1000 calorie deficit.

I go under my calories some days but try to stay within reason. If you are new to measuring it can give you a little wiggle room while you get used to it.

What she may have been referring to is the average deficit of 3,500 per week to lose one pound. As for going under, it's fine to go a little bit under provided you're getting all the nutrients you need and getting at least the recommended 1,200 calories.
That was one of the things I liked back in the old days of WW. It would give you guidelines that fell in line with the FDA Food Pyramid, or whatever they're calling it this month.
Granted there were days you could get your 4 oz. (or whatever amount) of protein with lean chicken or fish. Other days the calories would be higher if I picked ground beef or steak. Same with the whole grains. Some days I'd eat a hearty bread, or a large portion of pasta. Other days, I'd have light bread, whole grain pasta, brown rice, etc. And so on for the other food groups. I could have a banana, or I could have an apple, or maybe a tangerine. Each counted as one serving even though the calorie amounts might vary somewhat.
Like someone else said, it's fine to be a bit under if you're allowed 2,000 calories, but not so much if you're only eating 1,200 to begin with.