Sculkerite is a new crystalized ore found in the Deep Dark biome, which is an alternative to Netherite, as rare as Ancient Debris in deepslate, but common in Sculk. Sculkerite is based on stealth instead of damage and defense, and is slightly weaker than Netherite. To begin the main progression of the mod, follow this tutorial:

How to Obtain Sculk Alloy Ingots

Step 1. Mining

Mine down to deepslate with a diamond pickaxe.

Step 2. Finding Crystalized Sculk

Mine until you find a cave with an Ancient City or the Deep Dark biome inside of it. Once you are in the biome, search for an ore which looks like dark blue diamonds, or sculk which is slightly glowing and has blue crystals.

Step 3. Crafting

If you mined Deepslate Crystalized Sculk Ore, craft the Broken Crystals into Sculk Crystals:

Once you have your Sculk Crystals, craft Sculk Alloy:

This mod is supposed to be played with JEI (Just Enough Items), but you can play it without any QoL mods.