Blueprints are custom weapons in Call of Duty that have special weapon skins and attachments already unlocked. Blueprints can be unlocked through Battle Passes, purchased from the store, or earned through challenges.
To equip a Blueprint, go to the Weapons tab in Multiplayer mode and select Loadouts. Choose a loadout and select a weapon. In the Weapon Select menu, if a weapon has a Blueprint, it can be equipped by clicking on the Blueprint to the left of the weapon, which can be seen below.
A big upside to using Blueprints is that players can use attachments for weapons that may have a high weapon-level requirement to use. For example, the MP-40 “Shredder” Blueprint pre-order reward has a VDD 34M Padded stock that is only unlocked at weapon level 43. This way, players can try out unique attachments and have an early advantage with weapons.
Like Modern Warfare (2019) and Cold War, Call of Duty: Vanguard Blueprints will be useable in Warzone.
For more Call of Duty: Vanguard guides, check out Call of Duty: Vanguard all Attachments explained on Pro Game Guides.