A sprint is a short running race. In a track and field competition there are generally three different sprint distances: 100m, 200m, and 400m. The original Olympic event, the stadion race, was a sprint of around 180m.
A sprint race starts out with the runners in starting blocks in their lane. The official will say "on your marks". At this point the racer should be focused on the track, have their feet placed in the blocks, fingers on the ground behind the starting line, hands slightly wider than shoulder width, muscles relaxed. Next the official will say "Set". At this point the runner should get their hips slightly above shoulder level, feet pushed hard into the blocks, holding their breath and ready to race. Then there is the bang and the race has started. The runner should exhale and run out of the blocks not jumping. The initial part of the race the runner is accelerating to top speed. Once top speed is achieved then endurance kicks in as the runner tries to maintain that speed for the rest of the sprint.
Sprinters should remain relaxed while running and move their arms in a straight back and forth motion. They should be focused on their lane and the track at the start and the finish line for the last half of the race or so.
The middle distance races are the 800m, the 1500m, and the 1 mile long runs. These races require different skills and tactics to win that the sprints. They rely more on endurance and pacing than just pure speed. Also, the runners don't stay in a single lane for the entire race. They start out in staggered lanes, to make the distance the same for each runner, but the race soon becomes open with no lanes and the runners must to pass around each other to gain the lead.
There are three main long distance races: the 3000m, the 5000m, and the 10,000m races. These races are similar to the middle distance races, but the emphasis is even more on correct pacing and endurance.
A hurdles race is one in which obstacles are placed at intervals along the track that the runners must jump over on their way the finish line. Typical hurdle races are the 100m and 400m for women and 110m and 400m for men. Timing, footwork, and technique are key in wining hurdles events. Of course you still need to be fast, but jumping the hurdles in stride without much slowing down is how to win in the hurdles.
Relay races are where teams of runners compete against each other. There are typically 4 runners and 4 legs to the race. The first runner starts with the baton and runs the first leg handing off to the second runner. The hand off must typically take place within a given area of the track. The second then hands off to the third and the third to the fourth. The fourth runner runs the final, or anchor, leg to the finish line. Common relay races are the 4x100m and the 4x400m.