The phrase "fire projectiles" means to launch or shoot objects through the air with force, usually from a device like a gun or catapult. Full definition
You are represented as a little red heart and you move the heart around as the enemy fires projectiles at you. (nonfictiongaming.com)
Even though it looks a lot like The Legend of Zelda, the way Isaac attacks is more along the lines of something you would find in Resogun, Geometry Wars, or Super Stardust HD, where the right - analog stick is used to fire projectiles in any direction. (shortpause.com)
Movement feels reminiscent of Flappy Bird while firing projectiles is automatic. (nintendoenthusiast.com)