Signal at junctions
Your signals should be used to indicate your intention to do something like changing your position or your direction on the road. They do not give you right of way.
Signals should be used in good time so other road users have time to react safely.
Approaching junctions from a main road into a minor road...
Decide in good time where you want to go, check your mirrors and get yourself into the correct position in good time, signal your intention to change direction, if you intend to turn left move closer to the kerb, slow down into 2nd gear as you approach the junction, look into the junction as you approach it and if it is safe to do so follow the curve of the corner (hug the corner)
If you intend to turn right check your mirrors and get yourself into the correct position in good time, signal your intention to change direction, move closer to the centre line on the road, slow down into 2nd gear as you approach the junction, look into the junction as you approach it, line up your front wheels with the centre line of the road you intend to turn into and if it is safe to do so turn into your driving position on the new road which is keeping left of centre of your lane. Avoid turning into the new road staying beside the centre line unless you intend to turn right again very soon.
Signals on roundabouts:
When intending to turn left usually the first exit, check your mirrors and get yourself into the correct position in good time moving over to the left of the lane (only when it is safe and legal to do so), signal left to show your intention to leave the roundabout at the next exit, slow down and get into 2nd gear as you approach the roundabout, look into the junction as you approach, and if it is safe, look to your left before proceeding onto the roundabout.
When intending to go straight ahead usually the second exit, check your mirrors and get yourself into the correct position in good time moving over to the left of the lane (only when it is safe and legal to do so), do not signal, slow down into 2nd gear as you approach the roundabout, look into the junction as you approach, and if it is safe, look to your left before proceeding onto the roundabout, as you pass beyond the point of turning into the first exit turn on your left signal to indicate your intention to leave the roundabout at the next exit.
Alternately
When intending to go straight ahead usually the second exit, check your mirrors and get yourself into the correct position in good time, (when there are two lanes approaching the roundabout you can also use the right hand lane to go straight ahead if the left lane is a left turn only or the left lane is backed up with traffic turning left and the right hand lane is not restricted to turning right only) do not signal, slow down into 2nd gear as you approach the roundabout, look into the junction as you approach, and if it is safe, look to your left before proceeding onto the roundabout, as you pass beyond the point of turning into the first exit turn on your left signal to indicate your intention to leave the roundabout at the next exit. Stay in the lane you are in until you leave the roundabout and when you are driving on the straight you can then check your main mirror and your left mirror, signal your intention to change into the left lane and when it is safe to do so, check your left blind spot and if it is safe proceed with the lane change.
When intending to turn right usually the third exit, check your mirrors and get yourself into the correct position in good time moving over to the right hand side of the lane, signal right as you approach the roundabout to show your intention to turn right at the roundabout. Slow down into 2nd gear as you approach the roundabout, look into the junction as you approach, and if it is safe, look to your left before proceeding onto the roundabout. Keep your right turn signal on until you as you pass beyond the point of turning into the second exit, turn on your left signal to indicate your intention to leave the roundabout at the next exit.