The item contains an extradimensional space, allowing you to store up to 5 Bulk (whether a single item or multiple ones that add up to that much Bulk) inside of it. The space’s capacity doubles with each Tier above 1, increasing to 10 Bulk at Tier 2, 20 Bulk at Tier 3, and 40 Bulk at Tier 40. The Bulk of any items stored inside the item’s extradimensional space does not count against your Carrying Capacity.
While an object is in your hand or you are touching it and possession of it is not contested by another creature, you can send it to the item’s extradimensional space with 1 Minor Action. You can recall an object from the space to your hand with a Draw action, following that action’s normal rules.
If you have the Quickdraw feat, all of the contents of the item’s extradimensional space combined count as being 1 Bulk total for the purposes of designating them for that feat, allowing you to quickdraw anything contained within it.
Items inside the extradimensional space are frozen in time - they do not experience entropy, combustion, spoilage, rot, or any other kind of time-based phenomenon while inside.
You cannot place living creatures larger than a grain of rice inside the extradimensional space; anything larger is left behind when the object is sucked into the space. Non-mobile plants and fungi, as well as embryonic animals (i.e. eggs), do not count as creatures and can be placed inside without issue. Corpses (that aren’t Undead) do not count as creatures anymore, and can also be placed inside without issue.
While you are Attuned to and wearing or wielding the item, you have an intuitive sense for what is stored inside of its extradimensional space. Only someone Attuned to the item can withdraw items from the extradimensional space or place items into it. Any items within the space remain inside of it when the item is not Attuned to a creature, which may cause Spatial Rings or similar objects that are recovered by adventurers to have interesting surprises waiting inside for their new owners to find.
You cannot place an item with a Spatial Enchantment inside another item’s extradimensional space - the attempt fails, like you were attempting to force the same poles of two impossibly strong magnets together.