Global and interface are two seperate commands..
Global is a command modifier just like facet, area, m (multi).
These modifiers are meant to be used in combination with another command.
[Global interface
[Area interface
[m delete
[area wipe
Etc...
Interface is a general command allowing you to interact with objects in the world, look at their properties, go to them, delete them, etc.
Interface accepts arguements such as types and conditionals, so it can be compounded with these arguements to limit what you interface with.
Examples:
[global interface where basecreature
Shows you all basecreatures in the world
[Area interface where xmlspawner
Shows you all the spawners within the box that you target.
And you are only limited by your imagination..
[Global interface where playermobile hits < 100
Shows you all players who currently have less than 100 hp.
Hope this helps! Its a broad command so if you need specific help, just ask.