The starter tent does not allow you to share items with a trusted friend. You need a crafted tent like the explorer tent, which requires fine carpentry skill to make.

All parties you want to access a crafted tent should be friends, and should set each other as trusted friends in the friends management window.

1. Add each other as friends first.
2. Each of you open the Character sheet (C key).
3. Right click lower left or right area of the character sheet, either the body or the hand, Manage, Friends.
4. Set friend(s) as Trusted, Update friends.

Your friend should be able to add and take away from the tent's inventory.

You can attach a lock to a crafted tent to add permissions.