Placing and wearing

Three placement forms position an entity when the story starts: in puts it inside a room or container, on puts it on a supporter, and starts in is how actors (usually the player) name their starting room. Two more lines dress and equip an actor. wears puts a wearable onto an actor so that the actor is wearing it from the start, and carries puts an item into an actor's hands as starting inventory, so the actor holds it but does not wear it.

create the seed packet
  on the potting table

  A paper packet of runner-bean seeds.

create Alex
  a person
  playable
  starts in the Greenhouse
  wears the straw hat
  carries the trowel

  Mud on your boots, dirt under your nails.

before the game starts
  change the player to Alex
end before

What a character carries is visible to the player but not reachable: you can see the thief's knife, examine it, and be refused in the story's own words when you try to take it, but you cannot simply grab it. Compose open-inventory on the holder when the player should be able to take from them — a friendly character holding something out, a horse with saddlebags:

create the pack horse
  a person, open-inventory
  carries the saddlebags

Note the disambiguation: on followed by an article is placement (on the potting table); on followed by a bare word opens a behavior clause (on the player watching).