Online Documentation for SQL Query for Oracle
After you have registered the required database(s) the corresponding node(s) appear in the DB Explorer tree on the left. If the Show Hosts option is checked on the Environment Options | DB Explorer page, the host nodes are also displayed in the tree (alternatively, you can use the Show Hosts item of the Database context menu for the same purpose).
To connect to a database, simply double-click its node (or select the database node in DB Explorer and press Enter). If the connection is successful, the database node expands into a tree of objects. Now you can navigate within the database objects and queries. Use SQL Assistant to get extended information about the currently selected object.