Genetics is the study of the living organisms known as genes, which are inherited from our ancestors. The purpose of these studies is to find out what elements of people are determined by their genes and explain how these aspects, or traits, are transferred from parent to child. Some traits are physical and you can see between members of a family. You might find that many people in a family have red hair or have similar bone structures. There are also traits that are not possible to see with the naked eye. These are things like a person's blood type, their likelihood of contracting certain diseases or their personality.
Many people know of the battle between theories involving nature versus nurture. This is the difference between the things that are determined by genetics and those that are more because of our experiences, upbringing, and environment. For example, a person might have several people in their family who are exceptionally tall. But this predisposition could be countered by poor nutrition as a child. Or, it could be nurtured by living a good life. This could cause that individuals genes to be outweighed by their experiences or they could compliment each other.
Genes are made up of DNA, which is a long molecule that carries a pattern of information. This is called a genetic code and is sort of the instructions for assembling and operating that person. As you grow from a child into someone who works for a executive software company or someone who is a stay-at-home parent your DNA will help to determine everything from your appearance to your personal tastes and attitudes.
A person's genes are created when the information from your DNA makes proteins into cells. A person has more than a trillion of these cells in their body and all of these come together to form them and keep them alive. These genes are copied over and over again as the cells divide within their life cycle. Inherited genes are the product of cells from the mother and father are copied and entered into the DNA of the child. They might mean that a child will follow in their parent's footsteps to become teacher due to a knack for selling or could mean that they inherit the same style of nose.
You can't talk about genetics without referring to theories of evolution. There are some traits that become more or less dominant over time depending on the environment and need for that trait. We can see this through the evolution of people throughout history. Generations living hundreds of years ago had more need for physical strength rather than mental intellect due to their need to do more things without the help of machines. While there are still strong people doing kickboxing or competing in the Olympics, the average person is likely not as strong as they were five hundred years ago.