https://www.gamespot.com/articles/fortnite-building-guide-tips-for-battle-royale/1100-6456657/

Since the launch of its Battle Royale mode last year, Fortnite's popularity has exploded. That's no doubt thanks in part to being free-to-play, but while it follows the same basic format as other games in the increasingly popular sub-genre, it does offer a unique twist with its building mechanics. At the press of a button, you can build walls, floors, and stairs, and that ability is key to success.