Hey I dunno if I can be help, I'm usually good at physically showing things not describing lol.
Roundabouts are easy if you take it slow and not a burden
You should always signal from around 40meters because they can give you minors for incorrectly signalling, literally when you see the roundabout signs or just before it signal or so and get in lane.
I assume you already know what lane to choose when leaving at the second exit, third exit etc for example.
If you wanna leave the second exit for example, you should straight away signal after you pass the first exit. So check the mirrors after the first exit, quickly signal and leave the roundabout, its quite intense because you gotta do everything fast.
edit: forgot you said you don't know what lane to be in.
http://c8.alamy.com/comp/B4GM3A/road-sign-primary-route-road-sign-at-a-roundabout-england-uk-B4GM3A.jpgI looked up a random roundabout sign lol so I'll try explain exit by exit.
Where it says shap, you always choose the left lane, no matter what, you signal left from 40metres and stay in lane, (easiest exit, self-explanatory).
Second exit to Kenswick: Always stay in the left lane again, do not signal, it is very important to not signal as you will mislead other road users you are going to the first exit (Shap). So when you get the chance to get on, immediately stay to the left hand of the lane, not the middle not the right, always the left as you go about the roundabout, when passing the first exit, check mirrors, signal left and exit.
Now the third exit, to Penrith: Get into the right hand lane as its towards the right a fair bit. Signal right from 40metres as usual, when getting on the roundabout, stay all the way to the right and keep going, now when passing the second exit which will be Kenswick, quicly check mirrors, signal left and literally exit.
Fourth, same as third, exact same steps.
Dunno if i explained correctly, but good luck and try to practise alot..