Can anyone explain cable risers?

Are you talking about those little stands you put you speaker cables on so they're not on the floor?

Yes i am certain the op is asking about the little stands to place speaker wire, or interconnects so they do not touch the floor.
The electrical field in the wires extends out of the cable for a distance, (in most cable designs).
If you have a special meter which can measure such fields, you can 'see' them around cheap powercords, and cheaper speaker cables (even plenty of expensive ones)
So the idea is you do not want that field to be interacting with something just on one side.
((It will mess it up... in theory of course))
Air is a GREAT insulator, and a great place to run a cable so the field is not messed with.
The idea is the cable riser can lift the cable into all air surrounding it, and cause the least damage too the field.
The very best idea for cable risers is to suspend the cable via thin threads from above.
That was first proposed by Enid Lumley, who should be given credit for the idea for cables.

Anyway, that is the theory. Whether YOU can hear a difference???
It may depend on your stuff, and your hearing.

Cable risers are for those are seeking "street cred" from their audiophool friends. You can bet your bottom dollar that NONE of the various recording/mixing/mastering facilities are suspending their cables during the making of a recording.

Nor do they place bags of rocks or crystals on their interconnects, speakers and such.

If folks would spend more time and effort acquiring the very best source materials to playback and fixing the response anomalies found in their listening room, they would be rewarded handosmely with a much better sounding system...

-RW-

Not something i worry about but some carpets are prone to static electricity which can only be bad.

Also, running wires parallel to each other and in close proximity over a distance is generally not a good idea due to em field interaction and risers are one way to avoid that.