Hi!
I have written a few tutorials on how to setup LXD on different hosting providers.
I do not cover yet Google’s platform but it may be helpful to have a look.
Your actual question is quite specific and you are asking about how to set up LXD so that it is accessible remotely from another LXD client. If you are new to LXD, you might not need to do that yet.
In any case, the Google Compute Engine (GCE) gives your VM two IP addresses, a private IP (10.x.x.x) and a public IP. If you really want to make your LXD installation accessible remotely by another LXD client, you need to specify that 10.x.x.x IP address in lxc config set core.https_address 10.x.x.x.x.
Then, in the LXD client you can set up a remote using the public IP address.
See a similar discussion about GCE and private/public IP addresses.