I don't see where I can put an item in the inventory automatically at the start of the game.

Objects 'in' the player start in the inventory. In other words, WhateverObject.parent has to equal the Player.

You can use the function AddToInventory() as detailed in the documentation to add any existing object to the Player's inventory manually.

https://docs.textadventures.co.uk/quest/functions/corelibrary/addtoinventory.html