This is typical of the main road roundabouts we have around here.
As you can see, the lanes spiral out from the centre. It is just a case of getting into the correct lane on approach (usually well signed, with lane markings to confirm the route you wish). If you do have to change lanes you should only ever have to go in to the centre, so you just have to merge into the newly starting lane, and as you are already in the centre you cannot have anyone alongside you.
If you do find you are in the wrong lane, and the traffic is busy and it is unsafe to change lanes, a good driver will just take the wrong exit, turn round, return, and have another stab at it.
Most roundabouts are just single lane all the way round, so you never have another vehicle alongside you.