If you are talking to ATC you will get a FIS - it's one of the basic services that you always get from ATC whatever the circumstances (the other is the Alerting Service). If you are talking to ATC you may also get other services, for example a Radar Information Service.
You will also get a FIS from a station using the callsign xxx Information - you'll also get an Alerting Service but that's all you will get.
In theory you often have to ask for a particular service from a RADAR unit although you may find you get offered something if it helps the controller. If you ask for a FIS that's all you'll probably get but what's available will depend on many factors such as how busy the controller is (and remember it's not always apparent from the R/T how busy he or she is!).
A RADIO station may sound very similar to a what is provided by an INFORMATION station but it isn't, and it isn't a FIS - don't worry too much about why, but in practice you may be wise to treat the info you get from a RADIO station with a bit of caution.
Some of the subtleties of what you get from different ground stations are rather complex bit I hope this helps - for the test you're not going to need to worry about this sort of stuff.
The basics are determined by the callsign of the ground station, if it's GROUND, TOWER, APPROACH, RADAR (there are a few others listed in CAP 413 as I'm sure you'll know) you're going to get ATC which includes FIS and Alerting. INFORMATION will give you a FIS and RADIO is really just a communications channel to let you talk to someone at the airfield - what you get is largely down to the person on the ground.
Just for the record, this is a 'UK answer'.