"Fractions" just means the number of sessions the radiation is delivered over. I had 30 fractions, so my treatment took 6 weeks (five sessions a week, Mon-Fri, for six weeks); other common numbers of fractions are 37 and 20. Everyone's RT is tailored for them specifically, so your treatment might be a bit different to someone else's.
The basic procedure (in my case at least) is that you go in for a planning session at which point they scan you and then tattoo three dots on you - one at the top of each leg and one in the middle, over the pubic bone. These are what are subsequently used to line you up correctly in the treatment machine. Then for each session I was asked to arrive at the hospital 45m before the time of my session and use a "micro-enema" to clear out my lower bowel (to minimize radiation damage). This took about 15m to work. Finally, 20m before my session, I had to empty my bladder and then drink three cups of water. This ensures that your bladder has a (more or less) measured amount of liquid in it during the procedure, which lifts it clear of the prostate and again minimizes radiation damage.
Radiation irritates the bladder and makes you want to pee a lot, so you'll probably be advised during the planning session to cut out caffeine and alcohol for the duration of the RT (both are bladder irritants, so make the side-effects worse). I was also advised to go on a low-fibre diet (no brown bread, etc), but don't change your diet without advice; you should be told all this during the planning session.
I really didn't find RT too awful an experience at all. The side-effects for the final couple of weeks were a nuisance (I had to make two loo-stops during my 40 minute journey to the hospital!) but I didn't experience any diarrhoea, I just started passing a bit of clear mucus. The side-effects reach their peak about 10-14 days after RT finishes, but in my case they then quickly eased. Within 6 weeks of ending RT they'd pretty much all cleared up.
Hope that's of some help, and please do ask if you have any questions!
Best wishes,
Chris