Hi Joe,
Great to hear you've got your board and 2413S.
Linking can be in one or both directions (one link makes a device a controller and the other a responder and vice versa). Others with more insteon experience than I have (and with better memories) may have different advice, but whenever I'm in doubt I create a link that's in both directions.
In general if the device has a set button (most do), then you hold for three seconds to put it in Linking mode (the LED on it will start blinking), then you follow up by doing the same to the device you want it to link to (if I remember correctly, I think the first device is the controller and the second is a responder). When the two devices are linked you'll usually get a audible beep of some kind, and the light on the first device you pressed will stop blinking. Then you create a link in the other direction by changing the order of the devices you put into link mode.
One note, the set button on the light switch isn't very obvious. It's a tiny little button underneath the paddle of the light switch. You kind of have to press it in with a tool of some kind (unless you're more coordinated than me). Another note about this little button is that if you have needle-nose pliers, you can also pull it out a small distance which is a way to reset the light switch. Last, if you want to put a light into link mode and are having trouble pressing that tiny switch (e.g. don't have a tool with you to depress it) you can also put the light into link mode by holding the paddle on for ten seconds (after which it starts blinking to indicate it's in linked mode).
Another final note... sometimes you go to put your second device into link mode and it just starts blinking (e.g. now you have two blinking insteon devices at once). This generally means that your two devices aren't talking to one another. Sometimes there's noise on the line, sometimes they're on different electrical phases of your home's wiring, or if they're wireless then the distance may be too great or too many walls separating them. Or sometimes you just try it again (link mode times out after a few minutes) and it works the second time. Sometimes adding a couple repeaters /accesspoints can make a difference to help bridge the connection (particularly the two wiring phases of your home), or for just a little more money you can buy a dual band plug in dimmer (or perhaps even the new insteon light bulb.. haven't tried this, but looks even cheaper).
Alan