Here's where I'm gonna explain how the new Factions core works. It's a quite normal experience, with some twists. Firstly, let's go over the Nexus.
Your Nexus is the most important part of your base. Place your Nexus with /f Nexus. With your Nexus placed, you now have access to the Faction Bank. You also have access to the Energy panel. If your faction runs out of energy, all of your claims are removed. You can add energy with Coins. The more claims you have, the more expensive energy is! Also, if another player manages to kill your Nexus, anything in your claims are free to be tampered with by other players.
Here's the fun part. Sieges and War Pieces.
War Pieces are obtained by killing players of other factions in the Wild. When your faction collects 15 War Pieces, you can start a Siege on that faction.
During a siege, blocks can be destroyed by hand, chests can be opened, and etc. It's free game for 7 minutes. When the 7 minutes is up, the siege is over and their base is protected as normal.
There are other new things of course, but you'll just have to figure those out for yourself :) Have fun out there.