INTR WING - (internal wing) transfers fuel to the fuselage tanks when in NORM, and prevents transfer from the wing tanks (or to the tanks when refuelling) with the switch set to INHIBIT.
My understanding is that this would likely be used to manage a wing fuel leak, from battle damage or other. Probably of limited use in DCS.
"EXT TANKS WING" and "EXT TANKS CTR"
External tanks will automatically transfer fuel unless: weight is on wheels, or the refuelling probe is out. Use STOP to prevent fuel from transferring from external tanks, or to stop them being filled during refuelling. Use ORIDE to force fuel to transfer when it would otherwise be inhibited (i.e. weight on wheels, or probe out).
Scenarios when you might want to use these switches:
You have 3 external tanks, and want to use fuel from the wing external tanks first, perhaps so you can jettison them. You could set "EXT TANKS CTR" to STOP, to prevent the centre tank draining, so that fuel is used from the wing external tanks first. You'd then set this back to NORM once the wing tanks are empty.
You need to extend the refuelling probe (maybe you have an impending hydraulic problem) for the remainder of the flight, but still have fuel in the external tanks that you need to get at. The fuel won't transfer in NORM, so you can use ORIDE to force it to transfer. Again, probably of limited use in DCS.
In short, unless you have some sort of abnormal situation you need to deal with, these switches are 99.9% of the time are going to be left in NORM; but at least this should provide some background understanding of their function.
Flamin_Squirrel's post in F18 Fuel system - finer details and operations was marked as the answer