With the following images, you can see how is simple the process of creation of a new database service.
Login on your Oracle Database Cloud Service account, then click on "Create Service"
A simple web wizard will appear, in the first task you must choose a "Service Level" and a "Billing Frequency", Oracle Database Cloud Service is the most complete of functionalities:
Now you can choose the version of the product:
Now you can choose the software edition:
Here you can choose user, password and how mani cpu and ram allocate for your service:
Remember to put a pub key for ssh communication:
[Oracle Cloud & SSH: How to generate private and public keys (pub & ppk)]
I have decided "None" in the Backup Destination field, because is a simple test environment:
If you Select a Backup Destination, you need a Storage Container.
You can see a summary of your choices and you can proceed with the creation :