Do you mean 3C or 3S?

Wiring packs is pretty simple:

If you want to connect in series, connect + to -. The individual cells must be the same size and capacity.

If you want to connect in parallel, first make all your series connections (see above). Take the two "sub-packs" you just made and connect the loose + ends from the two packs together, then connect the loose - ends together.

When you've got prebuilt packs the best thing to do is make wiring harnesses to make the connections. That way the packs can be pulled apart for other purposes.