It's hard to describe a box pass in a few sentences. Here's a link that kinda describes the idea behind tradking cigars (a box pass):

Equal puts / takes

Some people view a box pass as a way to get a bunch more smokes than were sent out - a means of developing a larger cigar collection without the pain of having to buy them. If that is your intention, you are going to be sadly disappointed. That's not to say that you won't get more than you sent out, but you really don't have any control over what people put and take. And generally, if you are not satisified with what someone trades, it can cause bad feelings (BIG flame wars)...

Therefore - I suggest before you start a pass - get to know people on the board and develop friendships. A friend is less likely to burn you on a trade than a total stranger. That goes both ways!! If you have something a friend wants, wouldn't you just generously give it to them? The same works the opposite way.

A pass is really a way for others to try cigars they probably couldn't or wouldn't normally get. ISOM's is a great example, but not all passes contain ISOM's - plus trading for ISOM's requires you to have ISOM's to begin with (generally, that is pass rules). There are generally rare and hard to find cigars in passes, if the host has a decent collection - or the particiipants are generous.

I'd suggest you watch the pass threads - see what others do - watch puts and takes - converse with the participants to learn why certain things were done (what the value of cigars are - why someone put one cigar and took another - etc.)... In general, develop a series of friendships. You reason for starting the pass will then be for the RIGHT reasons - you'll see!!