The Arcane Codex- Healing Zone is one of six codex's which aid the player in their fights or general exploration. Using the Arcane Codex- Healing Zone will summon a 9x9 area centered at the cursor position (so it goes 4 tiles in every direction from where it's "core" is summoned).
This zone specifically greatly increases health regeneration when standing inside of the zone, this buff will carry on for 3 seconds after the player leaves the zone.
Do note that the Arcane Codex- Healing Zone requires a sentry slot to work and that the player is able to summon multiple Zones at once.