This doesn't add anything directly - instead this adds 3 base packages that mods can use to transfer items and fluids between blocks.

Quick overview (for developers):

Attributes: These are available on blocks that implement "IAttributeBlock"

Item and fluid management are both based around 5 similar attribute classes: ItemFixedInvView, ItemFixedInv, ItemInvStats, ItemInsertable, and ItemExtractable.

More details can be found on the wiki.