Set or edit your goals
From the home page, click "More," then click "Goals," then click "Calorie & Macronutrient Goals." I honestly don't pay attention to any of the other goals on this page.
Now that you're on this page, you can edit your goals. If you have a coach, use the goals that your coach gave you. If you do not have a coach, you can use a number of different calculators to try to figure out where to start.
Here's what I recommend you do: take your bodyweight and multiply by 12. To keep it uncomplicated (we could get into some serious math, but I'm not going to go there right now), start your macros at 35% Protein, 40% carbs, and 25% fat. That'll give you a starting point.
If you have a coach, they can help you understand whether you need to edit your macros as you continue down your fitness journey. [Sign up for coaching]
How to use the diary
How to enter food
From the home page, click "Diary." This will bring you to a screen that you will use to track your intake that day. You can plan for tomorrow, or look back at yesterday by using the arrows at the top of the page.
To add food, you can either click the big + at the bottom of the screen, or you can click the "+ Add Food" under an individual meal.
Once you've done this, you will search for the food you are planning to eat. Luckily, this tool has a lot of restaurants, packaged goods, grocery items, and produce ready to go in the database. You can also click the little scanner icon at the banner if your food item has a bar code. That will automatically look it up for you.
Pay attention to serving size and number of servings.
Once you've found the food and entered the right serving size, click the check at the top right corner, and that food will be added to your diary.
How to check what you have left/so far
From the diary page, scroll down to the very bottom and click "Nutrition." This will bring up a page that shows you how many grams of protein, carbs, fat, and fiber (these are the only ones I pay attention to) you have eaten so far, what your goal for each of them is, and how many grams you have left to reach your goal.
Tracking/planning macros is like a fun little math puzzle. It's fun to see what you can eat to fit your goals at the end of the day. And it's especially fun to do poverty macros (mostly lean protein) at the beginning of the day in order to plan a splurge meal like pizza or pie.
This is why counting macros is called flexible dieting. Yes, you do want to try to eat mostly whole foods and get your needed 25g of fiber each day. But we're all human, and sometimes we want pie. With macros, you can go out with friends, eat your pie and not have to worry about gaining weight, as long as it fits your daily goals.
I do not enter my exercise into MFP because I plan my macros for my exercise. If I enter exercise into MFP, it changes my macro goals automatically, and I don't want that.
You can also track your water with MFP. Personally, I prefer tracking my water with the app Waterlogged. But that's just me.
Hopefully this was a good starting point for people new to tracking. Please let me know if you have any questions, or if anything wasn't clear.