Long distance running is defined as running at least for 5000m or more. It requires stamina, tactics and long term training to hold pace for a longer time.
To run one of these distances can be a good starting place for you. If you are already able to run them try to aim for under 25 minutes on 5km, under 50 minutes on 10km and under 4 hours 30 minutes for the marathon to challenge yourself on time.
Beginners usually make the mistake of overpacing themselves in the beginning of the run. Always remember that you have to maintain pace through the whole run to finish it and hit your time. The longer you run, the harder it will get for you to maintain the same pace. Think of it like holding a full bottle of wine in front of you with a stretched arm. The weight stays the same, but the longer you keep the bottle in the same position, the harder it will get.