Explanation/Reference: https://docs.cloud.oracle.com/en-us/iaas/Content/General/Concepts/regions.htm

Explanation
When you sign up for Oracle Cloud Infrastructure, Oracle creates a tenancy for you in one region. This is your home region. Your home region is where your IAM resources are defined. When you subscribe to another region, your IAM resources are available in the new region, however, the master definitions reside in your home region and can only be changed there.
When you subscribe your tenancy to a new region, all the policies from your home region are enforced in the new region. If you want to limit access for groups of users to specific regions, you can write policies to grant access to specific regions only.

Explanation
Oracle Cloud Infrastructure Compute lets you provision and manage compute hosts, known as instances You can launch instances as needed to meet your compute and application requirements. After you launch an instance, you can access it securely from your computer, restart it, attach and detach volumes, and terminate it when you're done with it. Any changes made to the instance's local drives are lost when you terminate it. Any saved changes to volumes attached to the instance are retained.
Oracle Cloud Infrastructure offers both bare metal and virtual machine instances:
1) Bare Metal: A bare metal compute instance gives you dedicated physical server access for highest performance and strong isolation.
2) Virtual Machine: A virtual machine (VM) is an independent computing environment that runs on top of physical bare metal hardware. The virtualization makes it possible to run multiple VMs that are isolated from each other. VMs are ideal for running applications that do not require the performance and resources (CPU, memory, network bandwidth, storage) of an entire physical machine.
An Oracle Cloud Infrastructure VM compute instance runs on the same hardware as a bare metal instance, leveraging the same cloud-optimized hardware, firmware, software stack, and networking infrastructure.

Explanation
Oracle Cloud Infrastructure is based on regions and availability domains.
A region is a localized geographic area, and an availability domain is one or more data centres located within a region.
A region is composed of one or more availability domains.
Each availability domain contains three fault domains.

Explanation
Oracle Functions is a fully managed, multi-tenant, highly scalable, on-demand, Functions-as-a-Service platform. It is built on enterprise-grade Oracle Cloud Infrastructure and powered by the Fn Project open source engine. Use Oracle Functions (sometimes abbreviated to just Functions) when you want to focus on writing code to meet business needs.
The serverless and elastic architecture of Oracle Functions means there's no infrastructure administration or software administration for you to perform. You don't provision or maintain compute instances, and operating system software patches and upgrades are applied automatically. Oracle Functions simply ensures your app is highly-available, scalable, secure, and monitored. With Oracle Functions, you can write code in Java, Python, Node, Go, and Ruby (and for advanced use cases, bring your own Dockerfile, and Graal VM). You can then deploy your code, call it directly or trigger it in response to events, and get billed only for the resources consumed during the execution.