KReporter edit mode opens in manipulate tab. This is where you decide which data will be displayed. Each report is based on a module. In order to decide which one to select ask yourself which data you want to display. Let's take an example: You want to list closed opportunities see their amount, which user is assigned to this opportunity and the account they are related to. The main information is based on opportunities. You will therefore select the Opportunities module in left top panel. Select root module first. Corresponding fields will be displayed in the left bottom panel. Use filter to find the right fields, drag&drop the fields you need to manipulate area. Modify the name of the column header if necessary.
Click on tree nodes to access related fields like Account name or Assigned User name.