Compound names are simply cards names with a "+" in them.
The plus sign divides card names into left and right parts. Creating a compound named card automatically creates a card for each of its parts (unless they already exist).
Suppose we create a card named Joe's Coffee+hours. It's name contains a "+"!
When we have a card with this name, we know that we have two other cards: one named Joe's Coffee, and another named hours. If you create a compound card and the parts don't already exist, Wagn creates them automatically.
Remember that Wagn names are unique. There can only ever be one card with a given name. For example, there can only be one Joe's Coffee card on any Wagn website.
If we were to create Joe's Coffee+location and Joe's Coffee+menu, they would both share the same left part (Joe's Coffee) with our original card, Joe's Coffee+hours. By the same token, if we created a card named The Bumpy Grind+hours, it would share its right part (hours).
This means that we can use naming patterns alone to start creating networks of information. With the above examples, Joe's Coffee is "plussed" to three other cards, and hours is "plussed" to two.
By following naming patterns like these, we can begin to organize card information in highly flexible ways.
There is very little "howto" involved in compound names themselves. All you have to do is use a "+" in the name, and you're using compound names.
In general, we do not recommend requiring casual site visitors to know anything about compound names. Most visitors shouldn't have to know what a "card" is, much less how to structure it's name. A good Wagneer will create a site where this kind of background knowledge is completely unnecessary for casual users.
However, compound names become powerful when you start using them in patterned ways. To do so, you will need to learn about formatting.