The Vesta provides 32 channels of discrete inputs. These inputs are intended to be connected to dry contacts - that is, electrical contacts which do not have any voltage or power source connected to them. Examples would be switches, microswitches, some thermostat contacts, snap-action thermal switches, and magnetic door and window switches (as used on alarm systems).
If you're not sure whether a set of contacts qualifies as 'dry contacts', check with a handheld Voltmeter (in both AC and DC settings) when the switch is in both positions.
In the Vesta, discrete inputs are provided in groups of four. Standard Cat5 (Ethernet type) cables are used to connect discrete inputs to the Vesta. A common use of discrete inputs is to monitor relay contacts in RI-1209 and RI-1210 sense relay boxes. There's an application note that covers an example of this.