How Do Arcane Focuses Work 5E?

An arcane focus is a Special item designed to channel the power of arcane Spells. A Sorcerer, Warlock, or Wizard can use such an item as a Spellcasting focus, using it in place of any material component which does not list a cost.

Is an arcane focus used up?

Your arcane focus will never be used up. Some spells consume their material components though and those spells have notes in their descriptions saying that the material components are consumed by the spell.

How does a focus work 5e?

A focus is just another way to satisfy the Material (M) component needed to cast a spell where it's required. If a spell needs a material component, you can use your focus instead. If the material component has a monetary value, for example a Pearl worth at least 100gp, then that specific material is still needed.