All depends on your current condition (overweight, skinny (like me) etc.).
You can start looking at BodyBuilding.com if you like (beware of all of the ads and articles pushing stuff):
Just do a search at the top on the types of exercises (Deltoids, Biceps, Triceps) and look over the articles. There's a lot of good advice amongst the tripe...
If' you are staring from "skinny", check this one out:
Very good site to get started building some muscle.
Basic advice, don't push yourself too hard to begin with. Focus on toning first, might even think about a little cardio (running, jogging, swimming) for a bit to burn off some "deadweight tonnage" and make sure you have some endurance. Do modest weights with more reps - let's say 10-ish kg (metric, since you are in the UK) and about 15 or so reps per set. If 10 kg is too much right now, don't worry, just drop it back a little and do what you can.
My general rule is, if it gets easy, you aren't doing enough weight. Move up 2-3 kg and do a slightly lower number of reps if you need to.
As to how often and when - 3-4 days a week and when it works for you. Some prefer 1-3 hours before bedtime, others, just after getting up. How long of a workout? 30 minutes to an hour, if you can handle it. Less than 30 minutes is probably not going to help much but - you can also just keep a dumbbell setup for a modest weight and do a few while sitting at the computer occasionally...