The Blueprint Library is a repository where a player may store a large number of Blueprints and (despite its name) Templates for later retrieval. Additionally, plans saved to the Blueprint Library are saved to the user's hard-disk, allowing them to transfer blueprints between worlds, or from SSP to SMP and vice versa.
A Stone Pick or better is required to retrieve a Blueprint Library.
To save a blueprint or template, the player opens up the Library GUI by right-clicking on it. Once done, the player takes the recorded Blueprint (or Template) they want to save and places it in the slot on the right side of the arrow pointing left. After a few moments, the plan's contents will be saved to the Library (and the player's hard-drive) for future reference. If there is already a plan sitting in the 'Saved' slot, the Library will stop at 100% and wait until the plan is removed before saving the next blueprint.
To retrieve a Blueprint (or Template), the player selects one of the saved plans from the list on the left, and places a Blueprint or Template sheet in the slot on the left side of the arrow pointing right. After a few moments, the Library will print a new plan out on the sheet provided.
The player does not need to use a blank Blueprint or Template, but using a printed plan will delete the previous design to write the new one.
WARNING!: Do not, under any circumstances, attempt to save a Template and write it to a Blueprint, or vice versa! Placing them in a Builder will crash Minecraft and irrevocably corrupt your Minecraft World!