As your description is unclear i am assuming you mean twin and earth cable. There are several ways but the two i find best depending on the situation are.1.Junction boxes ranging from 20amp to 30 amp these are for 1.0,1.5 and 2.5mm squared twin and earth cable.2. through crimps of various sizes ranging from red for 1.0,1.5mm squared cable for lighting blue for 2.5mm for power for sockets and yellow for 6.0mm for cookers.I also use a ratchet crimper to make sure these connections are tight and then i use insulation tape over them after to make sure they are fully insulated.But this depends on what you need to do and where.You have not said wether they are under floorboards or cables buried in the wall your post is a bit vague more information would help.
There are many ways of joining cables. From the resin filled cable joint to a simple junction box.
Consideration must be made as to if the cable needs some form of grip, can it get damp, will it be accessible?
Also voltage and location and size.
The method of joining a 150mm steel wire armored cable to be buried under ground is very different to joining the cable going to a door push.