Redstone basics in Minecraft: dust, repeater, comparator, observer
A Redstone Comparator (3 Redstone Torches, 1 Nether Quartz, 3 Stone) takes a signal from behind and another from the sides.

Nether Quartz is a white crystal mined from Nether quartz ore.
It is obtained in the Furnace from Nether Quartz Ore (other recipes also exist).
Ore veins are common in the Nether and give experience as well. Quartz crafts the Redstone Comparator, the Observer and the Daylight Detector, and four make a Block of Quartz. It also colors armor trims.
Nether Quartz Ore → Nether Quartz
// Slots with several items cycle through every accepted option.
A Redstone Comparator (3 Redstone Torches, 1 Nether Quartz, 3 Stone) takes a signal from behind and another from the sides.
emeralds for Stone and Nether Quartz, Terracotta
In a Furnace: 1 × Nether Quartz Ore gives 1 × Nether Quartz. In a Blast Furnace: 1 × Nether Quartz Ore gives 1 × Nether Quartz. It can be found as loot in Bastion Remnant. Bought by Villager: Mason (Expert). Bartering: Piglin.
It is the key crystal of redstone components and quartz blocks. It is an ingredient in 6 recipes, made at the Crafting Table; for example Granite, Observer and Block of Quartz.