You access the Developer Studio features from the Developer Studio Dashboard. From the Eclipse Welcome page, you can click Open Dashboard, or if you are already viewing the workbench, click the Developer Studio menu and choose Open Dashboard.
When the dashboard appears, you can scroll down to see all the available features. Click a link to create that item.
In addition to using the dashboard, you can choose File -> New -> Other and select an item from the WSO2 category.
If you have an existing project, you can right-click the project, choose New, and then choose one of the WSO2 options from the menu.
For an introduction to working with Developer Studio, see Quick Start Guide.