You need the user guide for your particular board, in order to discover the pin assignments for the various devices on the board. Either you can find this on the internet using the board name or part number, or you may as well throw the board away.
A very common Spartan 3E board made by Digilent is linked below. They have the user guides on their website. But of course, if this is not your board, it is useless.
I advise that you NOT use a Spartan 3 for any purpose. The reason is not "just" that it is old, but that it had some problems with the internal power regulation and would sometimes give erratic results. If two many gates switch at once, internal noise will corrupt some bits. I spent a couple of years using these boards and found they would work only sometimes and only if a small percentage of the programmable memory was used.