The Cells need to be soldered together in what is called Series, that is, the positive side of each cell connected by tab wire to the negative side of its neighbour (see diagram)
To achieve this the (untabbed) Cells all need to be tabbed, that is to have flat Tab wire soldered to the front (negative) side and then to the back (positive) side.
Buy a roll of the thinnest Resin Cored Solder you can find.
Dick Smiths (Aus) sell a good 0.8mm solder at a reasonable price.
You may not find flat tinned Tab Wire at your local Electronics store so eBay (USA) could well be your best place to look. That's where I got mine.
It's a flat copper wire tinned on the outside and comes in several thicknesses. I found the thinnest one easier to solder to the Cells.
"A Resin Flux Pen".
This is a Must have.
Try your Electronics store. If they haven't got one they should be able to get you one.
If they can't a Google search will find you a supplier.
The Soldering Iron
Preheat your Soldering Iron to about 270 degrees C. and give it a wipe on the damp sponge that comes with it (a small natural sponge that needs to be just dampened with tap water).
Cut Your Tab Wire to Length.
This is a good time to calculate the number of (eg. 72 for a 36 cell panel) and the length of the tabs you'll need and to cut them to length (or a bit longer....just to be on the safe side).
The length will need to be almost twice the width of the cells to enable it to cover all of the Front Bus and to go across the Back Busses (there will be at least 2 directly behind each Front Bus).
A Small Fan.
You'll be doing a lot of soldering.
The fumes that come off the Resin Flux and the Solder as you're working may not be harmful but.......I'd rather not take the risk.
I mounted a small 12v fan (out of a PC) on my soldering board to take the fumes away from my face.
I made a foot operated switch for it and run it off a transformer.
Holding Your Solder.
You'll be holding your solder for long periods of time.
The Solder contains Lead.
To be on the safe side I run the solder through a thin (red) plastic tube. This acts as a Handle and stops contact with the solder while still allowing easy use.