Look at the docs contained in that link and do a search on the board for 'HLC' (you'll need to use 'HLC link' or 'HLC light' or something, playwith it a bit - HLC is too short by itself (but would be my preferable search if allowed).
There have been several threads discussing the process.
If you are just starting out, then by all means use the HLC scheme - it's much easier than changing a full install to fit the HLC convention.
Any UPB switch can be used with HLC. You have to program non-HAI switches in UpStart.
HLC is merely a structured allocation of links into groups or 'Rooms' that is programmed into the Omni.
When the Omni sees a link that belongs to a room it sends a status request to update the status of each UPB unit in that room.
These don't have to be physical 'Rooms'.
I have a 'Room' for all my bathroom fans for example, even though they are scattered throughout the house.
Also the links, Scene A, B, C, D, are hard coded into each 'Room'.
But their functions are not. That is controlled based on how you program the UPB switches in UpStart.
So in my 'Fans' room, I have Scene A control the Master Bath fans, Scene B control the Guest Bath, Scene C control the Powder Room and Scene D control the Laundry Room Fan.
ALL ON turns them all on and ALL OFF turns them all off.
Whenever one of the 6 scenes for the room is executed, the Omni updates the status of all the fans.
For the scenes I simply don't set up the fans to respond to the links that don't apply.
If Scene A is Link 3, I setup the Master Bath Fans to turn on for Link 3, but not the others.
The status for all units is still updated when the link executes.
The Omni expects the fans to respond to the links so it asks for status, but the switches only react to the links they are programmed with.
It is a very powerful and flexible system once you examine it.