Hi,
please run the installation again and choose database platforms you wish to work with. If you installed Toad Data Modeler from Toad for Oracle Suite, support for Oracle databases was installed by default.
You can also open Control Panel and change the installation from there.
Select Toad Data Modeler from the list of installed applications and click button Change. The installation process should start...
Choose Modify and in next step you will be able to select the database platforms.
Good luck!