Now, you're ready to actually do your experiment -- how exciting! Follow your procedures and record any data or observations you make in the notebook. Also, remember to take pictures of your experimental setup, trials, and anything else you may want to report back later on. Have fun!
Coins have a 50% chance of either landing on "heads" or "tails." If you flip a coin once, it will land on one of those two sides, meaning that the odds of it landing on that side were 100%... but we know that isn't true. If you flip a coin enough times, the rate at which it lands on one side will get closer and closer to 50%, the "true" amount. This is why it is important to run an experiment multiple times! It helps make sure that a data point doesn't exist because of an error or random flaw.
A good rule of thumb is to do an experiment around 10 times, but that number can vary on a case-by-case basis.