Collection variables are used to store multiple values of similar data types. For example, a group of e-mail addresses. Once you have populated a collection variable with values, you can use it throughout the Flow.
An example business scenario: Helina Jolly is working as a system administrator in Universal Container. Currently, she is developing a Visual Workflow and wants to create a variable to store customers' e-mail addresses to send out an e-mail to them.
To create a collection variable in your Flow, follow these instructions:
Navigate to Setup | Build | Create | Workflow & Approvals | Flows.
Click on the New Flow button; it will open the Flow canvas for you.
Then navigate to the Resources tab, and double-click on Collection Variable available under the CREATE NEW section. It will open a window for you, where you have to enter the following details:
Unique Name: Enter the unique name. The name must begin with a letter and use only alphanumeric characters...