Open the Chat Window. The easiest way to run a command in Minecraft is within the chat window.
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Type the Command. In this example, we are going to summon a fireball in Minecraft Java Edition (PC/Mac) 1.20 with the following command: /summon fireball ~ ~1 ~
they spawn within a certain radius of the spawner, which is within the bounding box of a nether fortress. But no, there does not have to be nether brick below them or the spawner for them to spawn. it depends whether you're playing java or bedrock.