Why the need for additional Project Web App instances
You probably realize a default instance of Project Web App is created upon signing up for the service in an Office 365 Portal. There are, however, many times in which an organization may want to create or provision an additional Project Web App instance. For example, an organization may have separate security requirements in project web app instance. One instance may have relaxed requirements and the other more granular and rigid. There may be a need for a development instance. Or perhaps one department simply wants their own instance with their own users. Whatever the reason, the Office 365 administration options give administrators the tools to create a new Project Web App instance for each specific need.
Office 365 Portal Administrator
Now when it comes to performing this action, a user with the appropriate Office 365 Administration access is required. This is usually some level of Portal Administrator. This is because the function is performed outside of Project Web App. Meaning, a project manager, team member or even a portfolio manager are not able to perform them. 
These roles are users within an existing PWA instance. in Project Web App they will typically organize tasks, perform resource management, view Gantt Charts and much more. Therefore seek out a Office 365 portal administrator for this task. And remember, it's not a Project Web App site administrator you need.
Project Online Site Administrators
Site administrators in Project Online are the users who can configure the Project Web App settings. They are capable of setting up many of the options in Project Web App. A short list would include setting up Active Directory synchronization, adding users, creating time reporting periods, configuring custom fields and much more. It is also the Project Online Site Administrator that will configure security in Microsoft Project Online for each instance. The security configuration determines how project managers, team members, and others will use the product.
Creating the new Project Web App site
There are two options for creating a Project Web App site. The Project Web App site may either be created as the top level site of a new site collection, or added to an existing site collection. Both cases require using the SharePoint Central administration features within the Office 365 portal. Note the details in the two bullets below to better understand which scenario would apply to you:
- Is there a requirements to have an entirely new/clean environment to begin managing resources and projects. If so, a new Project Web App site as the top level site in a new site collection is your best path forward.
- In contrast, perhaps you have an existing SharePoint task lists that you would like to add Project Web App functionality to. Consider adding a Project Web App site to them.
Project Web App instances are created in a SharePoint content databases. The previous architecture requiring four Project Web App databases for each instance is no longer going to occur. In addition, you are no longer directly dealing with manage service applications, SQL Server, and a Web Application. These types of functions are in a way handled behind the scenes. SharePoint administration is very different in a "Server" environment compared to an "Online" environment. Note: the process to do this varies greatly between Project Sever and Project Online. The focus of this video is Microsoft Project Online.
Microsoft PPM ready and capable!
Once your new Project Web App site is created Microsoft PPM capabilities will be available. It is at that time project managers may create enterprise projects to manager and track project work and resources. 
Project Managers in Microsoft PPM are the users who will create projects, maintain task lists, query resource availability and much more within Project Online. Using MS Project Professional to create a project in the new instance will be one of the very first a project manager may perform. This would include situations where you are Importing a project). Microsoft Project is a robust tool for task management, dragging and dropping users in the Team Planner. Creating a shopping list? MS Project may help there too! The product also integrates well with other Microsoft Office products. Many will also manage resources. The resource management capabilities in Microsoft Project Online provide robust functionality to understand an organizations ability to take on new projects. This is typically a complex data point to determine without a PPM solution. Whether it's planning your day or managing a team of resources, the project management tool has many features and functionality. Each to assist you with managing and tracking work.
This Video
Amanda Kuhlman will walk through the process of creating a new Project Web Access instance in this video from beginning. Every step will be discussed, options presented, in order to provide viewers the information necessary to perform this task on their own.
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