Engram points are given to you every time you level up your survivor and are used for unlocking new recipes from which you can craft new items. Blueprints on the other hand allow you to craft the corresponding item without having to unlock it through engrams. You will be able to craft it even if you do not meet the level required to unlock the item.
Remember though that even if you find a blueprint you will still need the necessary materials to craft it. For example, you will not be able to craft the item for instance if you just so happen to find a high-level blueprint early in the game and you do not have the means to gather the necessary resources.
Blueprints are found by either giving Artifacts to an Obelisk as Tribute, or completing Pursuits.