It is very much like any differential input. All inputs require two
nodes, because any signal voltage has to exist with respect to some
reference voltage (and any signal current that goes in one path has to
exit from some other path). Single ended signals use a common node
(ground) as the second node. Differential signals carry information
as the difference voltage between two nodes, regardless of the average
voltage on the two nodes with respect to ground.
The amplifier responds (ideally) to only the difference voltage
between the two nodes, and ignores any common (average) voltage.
A very simple example of a way to convert a single ended amplifier
input to differential input would be to add an isolating transformer
to the input. The signal is applied across one winding (that is
isolated from any ground connection, or has its center tap grounded)
while the secondary has one end grounded and the other end tied ot the
single ended amplifier input.
This works fine for AC signals, but won't work for DC.