Getting an Instance
Most of the API is accessible via net.mathias2246.buildmc.api.BuildMcAPI.
You can get an instance by using the provided events. You have two recommended options available based on your needs:
Alternatively you can use BuildMcAPI.tryLoadAPI(). This approach is not recommended. This will crash your plugin if BuildMC-Core is not loaded before your extension. The method uses the Bukkit Services Manager to get an instance of the plugin.