Behavior packs, usually shared as add-ons, change how Minecraft Bedrock Edition plays: new mobs, items and blocks, changed game rules or scripted features.
This category (its address uses the British spelling, behaviour) lists add-ons that creators publish on Bedrock Graphics. Add-ons are turned on per world, and many need a matching resource pack, which is usually included in the .mcaddon file. Every project is reviewed by staff before it is listed.