Blaze rods are something used for fuel in furnaces or brewing stands. Most of these things require you to craft it into blaze powder by putting one blaze rod into the crafting grid in your inventory and taking the two blaze powder out. Creating brewing stands costs a blaze rod, not powder. It’s also used to make eye of ender, which is crafted using an ender pearl and a blaze powder.

Blaze rods can be obtained by fighting blazes from fortresses in the nether.