If you strip the insulation from the live or neutral conductor of 6mm² T+E cable, you will find that, rather that having a single ('solid') copper core (as would, for example 2.5mm² T+E), it is 'stranded', consisting of seven small copper cores twisted together.
A spur is a branch, using a single cable, from a ring circuit. Since the ring itself requires two cables to be connected to a socket, if a spur also originates from that socket, there will be a third cable - hence three conductors into each of of the terminals. A conduit box is what it says - a box designed to have conduit (plastic or metal piping, to contain cables) connected to it. I wouldn't worry about 'figure of 8 circuits' - the phrase refers to two rings joined together at one point (hence a 'figure of 8' appearance) - but it's not something that should be done (not the least because it makes testing a nightmare!) - I think it was mentioned as a 'tongue-in-cheek comment (since it would require four cables meeting at one socket, hence four conductors per terminal)!
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
