how to bridge speakers

Please clarify what you are trying to do...

You dont bridge speakers. You can wire them in series, parallel, or series-parallel configuration.
If you are talking about bridging the ouput of an amp, that is different. To bridge an amp, usually you will only use the positive terminal from one channel, and the negative from the other. There are different ways to bridge an amp, make sure you follow its instructions, though, cuz not all are the same.