series is with the positive of one cell soldered to the negative of the next, so it looks a bit like this:
+-+-+-
-+-+-+
this adds the voltage together, so a 6 cell ni-mh pack wired in series is 7.2 volts
parallel is with the positive wired to positive, negative to negative, so it looks like this:
- ---- -
++++++
this adds the capacity together, so 6 4500mah ni-mh cells will make a 27000mah 1.2v pack.
you can have different layouts of this, so a 6.6v 6900 pack is (i think, i'm not sure) 2 packs of 3 cells in parallel wired in series. so it would kinda look like this:
-- - +++
+++ -- -
so if you treat each parralel pack as one cell it would look like this:
+-
-+
hope that made sense...