Its very very difficult to pin point what to explain as there are so many roles availible, I can understand your frustration n making a choice but honestly what you read about in the glossy mags is often not what you end up doing.
Look at it this way, if you want to be at the "fighting end" (and I say that very loosely) you can do things like Gunnery (working on the guns, loading firing, caming up, driving etc) or Air Defence ( same as gunnery except you fire rockets at planes) or even Depth Fire (again like gunnery except you fire even bigger rockets at ground targets) The driving side speaks for it self, except some of it is in armoured tracked vehicles or perhaps large trucks (get you LGV lic for that). I am unsure where Observation Posts fall as I feel its a subtle mix as it can be a bit techy, but not overally. OP's work in small teams at the front line bringing down gun fire on targets, this tends to be one of the most favoured roles and most progress there rather than go straight in
Tech trades teng to be Signals (setting up radio masts, talking on the radio, sending and recieving fire orders etc) Signallers are everywhere in the Royal Regt, there are other trades that I friegn form talking about as I have been out a number of years and don't want to give you duff advice, lets just say the Command Post (and/or Co-Ord Centres) are where a lot of the trades are. Maybe not a lot of banging stuff like at the guns, but you remain busy and it streches your mind. Other Tech trades ate the STA assets, these are the differnt methods of locating targets for the guns to fire at less OP's. These jobs (Radar, Sound Ranging, UAV) involve a lot of setting up tech equipment and monitoring, some areas a good grasp of IT is useful.
So mate the question is what do you fancy ?!?
First thing you need to ask your self is why you want to join the RA and then take it form there, if you have any specific questions then please ask (PM me if you want) I will answer any question no matter how bone you think it is
am at larkhill at the moment mate and trust me - dont worry about technical or crewman techinical as you decide what reg you join on your phase 2 visit from phase 1 (a 10 min slide show followed by 5 mins to pick your regiment, therefore setting you up for your career).
if you like the idea of acertain aspect of artillery then stick with it or if you just wanna join artillery get to phase 1 and learn about it all from there - i was in same position as you but soon realised that the the two meant nothing really