Version: Spigot 1.12.2 (vanilla-compatible)
The WorldEdit selection wand is configured to be a Stick. With it selected, you can select cuboid zones (3D rectangles) by left clicking one point and right-clicking the other.
(WorldEditCUI is a client-side mod that simplifies this process by showing selection zones on your screen. As well, the //expand, //shift, and //contract WorldEdit commands may be useful to further adjust a specific selection.)
Then, use /rg claim <name of your base> to create your claim.
You can also use /rg am <other player's name> and /rg rm <other player's name> to grant and revoke build permissions to others respectively.
To allow anyone to enter your base and interact with items (but not build or open chests), use /rg flag <name of your base> use ALLOW
You can use /home to return to your last bed spawn, and /spawn to return to our lovely spawn island.
Some regions also have teleport points defined; if you are a member, you may access them via /rg tp <region name>.