Clicking on the 'Fields' button of the Project section allows you to add, modify or delete custom fields for your projects. There are no limits to the number of custom fields you can create.

From the above screen you can give the new custom field a Field Name, Description, and DataType.

Project Association

This is a mandatory field and after selecting a data type, you can pick and choose which projects have access to the custom field. By using the drop down, you can select one or multiple projects that the custom field belongs to or you can simply select the check box to include the custom field for all projects. 

This is beneficial in that you can create and define custom fields for a specific project or a specific set of projects.

For example, you can create a custom field that is used only for project A and any other project cannot use that custom field. You can even select multiple projects but not all projects. If the custom field is defined to work for project A and B, it will only work for both of those projects but not any other project.