To get started, there are a few words to know

Health Literacy: this is your ability to read, understand, and make decisions about your health. Being able to do this will help you take better care of yourself and others.
Health: your mental, physical, and emotional state
Barriers to health: the things that stop or slow you down from seeing a doctor, getting the medicine you need, understanding why medicine helps you.
Do you know why people experience this? That's right. There is no single reason, but many. Some people can't afford help, they don't know when or how to get it, it may be their religion or culture doesn't support it, or perhaps it simply does not exist in the community. The effects of this can last a lifetime. It is a hard and complex issue, but important to look at because everyone deserves to get the help they need.
Nutrition: the food and drinks you consume. Ideally, this is a balance between carbs, proteins, and fats. Every individual's nutrition may look different and that's ok. The important fact here is that it provides the energy and building blocks for daily living.
Calories: the energy your body gets from food and drinks. How many calories you need will depend on factors like your age, sex, how often you exercise, etc.