If you wanted to create a subpage called Tiger from the parent page called Big Cats you would:
1. make sure you are on the parent page node, in this example Big Cats, then 2. create a new wiki page in the normal way by using the two square brackets but precede the new page name with a slash ("/"). For example:
This will display the link with the slash ("/") like this: /Tiger, which may be a bit confusing to some readers.
There are two ways you can fix this. Either
1. Add an extra slash: Tiger at the end of your link (which "tells" the wiki software not to display the preceding slash) or 2. create a piped link, for example: Tiger. This is useful when the page link contains a number of slash arguments, or you want to display a more descriptive title to the user. Both of these methods will result in a link like this:
This is actually a subpage of the current page.