Increasingly, many modern cameras have interval shooting built-in, so spend some time with your camera's manual to figure out how it works.
When you feel ready to photograph star trails, we have a guide on how to do so and the best intervalometers, which you may find useful. An intervalometer does what the name suggests—it releases your shutter at regular predefined intervals to capture the night sky's 'movement' throughout the evening. Increasingly, many modern cameras have interval shooting built-in, so spend some time with your camera's manual to figure out how it works.