Also, that post on stackoverflow is about LXC, not LXD. See Comparing LXD vs. LXC for the differences.
An easy way to figure out whether a tutorial is about LXC or LXD, is when they use commands like lxc-start (with dash) (these are old LXC), or whether they use commands like lxc launch ubuntu: (with space) (these are the new LXD).
There are two main repositories with containers images, ubuntu: and images:. To see what’s in them, run lxc image list ubuntu: and lxc image list images:.
As you are learning, go through the posts at LXD 2.0: Blog post series [0/12] | Stéphane Graber's website to get a thorough idea on what you can do with LXD.
Also, see at The LXD tutorials of Simos for my entry-level tutorials.