i guess google didn't help? there is tons of links and pictures that explain it in detail...
you strip two wires (call them A and B), cross them at stripped part,
wrap wire A around neck of B and repeat the same for the other side.
solder them together. this provides good electrical connection and
mechanically solid system.
this connection makes sense only when wires are too long to replace
with single new wire (power line), wires are exposed to mechanical stress
(hanging for example) but not flexing, you are using single wires (splicing multiple
wires like in multiconductor cable doesn't work because i would like to see
genius able to make all 18 or 25 splices in a multiconductor cable
exactly same length so that they all share same tensile strength after
repair), you don't plan to separate them ever again (sure you can cut the
connection but every time you do it, wires are shorter and shorter...).