If you do use a pair of strobes with equal output, then you will also need to make an exposure adjustment to compensate for the doubling of light on the subject. If you do reduce the output of the second strobe, exposure compensation may not be necessary. Slave strobes require no connection to the camera. A sensor in the front picks up the light from the main strobe, which triggers the slave to fire. Since light travels so fast, both strobes will fire in the time it takes the shutter to open and close.
Slaves work best when close to a relatively large subject area.
Otherwise the slave won't reliably pick up the reflected light from the main strobe and will not be triggered. You can also connect both strobes to a T-connector. In this case the camera will trigger both and you don't need to worry about the second strobe not being set off. Paired TTL strobes can also be used. Since both will have the same light output, you can position the second one farther away or cover it with a white diffuser to reduce its output for more natural lighting.