The word meal means any time when you eat a large amount of food. There are typically 3 meals per day - breakfast (in the morning), lunch (mid-day), and dinner (at night). A snack is a smaller amount of food (for example, a bag of chips or a piece of fruit) and you can eat a snack anytime.
In American English, dinner and supper are the same - both are used to describe the evening meal. However, in some cultures, the word supper is used for a light meal served in early evening, and dinner may be later in the night.
If youve read the chapter once, theres no harm in reading it one more time. Reading it all over again helps you remember the information. Just make sure that you understand what youre reading so its easier for that information to switch over into your long term memory.