Do a search on YouTube for "DJI Spark range extender". You will find a lot of information and demonstrations on how well they work and how to use them properly. Please, do yourself a big favor and watch a lot of YouTube videos on flying your Spark before you go out to fly. It could mean the difference between a great experience or a great loss. These drones are not toys and should be flown with great care for all reasons and if you start out knowing what to expect, you will have a much better time flying it.
I have to ask this though. Is this your first drone ever?