First get some solar sells. Solar Cell Grab BagElectronics goldmine Solar cellsEbay
Thats just a few examples of where you can get solar cells, but it gives you a start.
First lest discuss parallel and series wiring
Parallel wiring increases amperage and voltage stays the same. Each cell in a parallel circuit is wired positive to positive and negative to negative.
Series wiring (mostly what you will use for solar cells} increases voltage and amperage stay the same. Each cell in a series circuit is wired positive to negative, the remaining positive and negative are you leads. You'll notice batteries in flashlights installed in series.
Now that you have your batch of solar cells we can get started!
First separate the cells in approximate similar sizes.
Remember if your wiring a group of cells together in series, the smallest cell in the circuit will dictate your panels amperage. Regardless of the size of your cells, each will produce about .5 volts. The bigger the cell typically the more ampreage you will get. So you wouldn't want five 6" cells with one 1" cell in series, because you would loose the amperage of the bigger cells and only output the amperage of the 1" cell. Basically try to keep the cells around the same size.
Most solar cells ( poly and mono crystalline) the positive side is the back of the cell and the negative is the front of the cell.