Every 2 hours you are able to claim a free basic spore bag. Opening the bag will give you 6 random spores. You can then drag these into each of the 5 grow spots.
The planted spores take 2 hours to grow into mushrooms. Harvesting mushrooms gives event points depending on the rarity of the spores planted. The Event points unlock personalised rewards based on what you do not have discovered in your flutterpedia!
You can watch videos to shorten the timers on the free spore pack by 30 minutes, but this can only be done once every 1.5 hours.
The final reward at the end will either be a decoration from a previous event, or glowbucks if you already have these all discovered.