DNNMenu is documented in the Navigation Web Controls Doc -- you can get it from the documentation page. It lists DNNMenu properties as well as a compare of DNNMenu and SolPartMenu. I found it difficult at first to figure out how to do what you asked as well since a few of the properties aren't listed in the tables. Here's an excerpt of page 21 that lists them:
This includes properties for Populate On Demand (PopulateNodesFromClient, ExpandDepth), which nodes to display (Level, RootOnly, StartTabId), and what text to use for Tooltips (ToolTip).
There are a few examples in the doc as well that help you figure out what they do too.