One question behind it all
Genetics is the science of inheritance: how living things pass their features on to the next generation. It grew out of one everyday observation that almost everyone has made — children tend to look like their parents. A puppy resembles its mother; tall parents often have tall children; a particular eye colour runs in a family. Genetics asks why, and answers it with surprising precision.
The short answer is that parents pass on information, not the features themselves. A child does not inherit their mother's actual eyes — they inherit a set of instructions that helps build eyes of a certain kind. That passing-on of biological information from one generation to the next is called heredity, and the act of receiving it is inheritance. The individuals that receive it — the children, pups, seeds, or seedlings — are the offspring.
Sameness and difference
Genetics has two faces. One is resemblance: why offspring look like their parents and like each other. The other is difference: why no two individuals (except identical twins) are exactly alike. That difference between individuals is called variation, and it is just as central to the field as resemblance. Without variation, every living thing of a kind would be a perfect copy, and there would be nothing for nature — or a dog breeder, or a farmer — to select.
A single observable feature — eye colour, plant height, flower shape, the ability to roll your tongue — is called a trait. Much of beginner genetics is the study of how individual traits are passed down and how they vary. We will spend the rest of this track building up the vocabulary to talk about traits precisely.
A scientist who studies all of this is a geneticist. Geneticists work on everything from why a wheat strain resists drought, to how a family's hearing loss is passed on, to how whole species change over thousands of years. The same core ideas you meet here scale all the way up.