Here at LunarRealms, we are a community-oriented network, and as such, we love to see our community members combine forces with other players of whom they trust to build amazing structures. Once you've created your first Claim, you've got a few sub-commands, and flags that you can use to customize your claim.
On most of our servers, you have to stand in your own claim and run the command /trust . Example: /trust VibrantRaven, this will give the specified player access to that claim.
On our 1.18.2 servers, the process is a little bit different. Simply stand in your Claim, and run the command /flan menu. After you've ran this command, a GUI will open for you where you can manage your claim. Now, in order to trust your friend, simply head over to permissiongroups, and either create a new one by clicking the Anvil, and type in a name, or select an already existing one.
After you've selected a group, click on the Anvil, and type in your friends name. If typed correctly, their head will appear in the list, otherwise you'll get an error message.
If by any chance they still cannot build, break or access chests, you might have to add some permissions to the group.
To do this, simply run the command /flan permissions group true. Example: /flan permission group Member OPENCONTAINER true. There's a list of permissions in-game for you to play around with.