Question about food

1 How do you usually call a food substance (one sort of food, ex. apples or sausage)?
2 Is '?structure? of meal' sounds well?
3 Is the phrase correct '?For? the first food intake you must have some apples'?
4 How is more usual 'the ?time interval? between meals'?
5 Is the phrase correct 'eat it ?with? 1-1.5 hour time interval'?
6 What is the synonym to 'not intensively'?

How to understand is a word countable or uncountable (do I have to use it with 'a'), for ex. 'food', 'foods', 'meal', 'meals', 'amount', 'amounts', 'area', 'areas'?