Essence is an addon that adds essence, which are used to craft spawn eggs and ores.
First thing, to get a mob essence you need a syringe. It is expensive but worth it, attacking a mob with it will give you it's essence. Supported mobs: creeper zombie skeleton spider enderman slime blaze magma block hoglin piglin chicken cow pig sheep drowned husk stray. Now that the spawner is CRAFTABLE BUT NOT Charged. You charge it by exp. Using mob essence will let you be able to craft it's spawn egg.
You can also get ore essence. You can get them by using the diamond ring. Use them to craft ores.