Processes can have different versions. This can be useful for many purposes - e.g., you want to start the same process for assignees in different states, and, when most of them need some actions started, some of them also require additional actions. In this case you can set up a process for most users, and create a specific version(s) with necessary properties for other assignees.

When you created a new process, it will automatically became a Primary version (1). To create another version, you can go to "Versions" subtab (2) of process details page and  click "Clone" menu item (3) at version entry:

The cloned process version will have the same name as source one (4), but it will be non-primary (see below) and inactive (5):

Click on version name link (4) to go to process builder (6). Rename version in process settings (7), make all necessary changes and activate it (8):

Now you can start process on new version when necessary.

By default newly created process has only one version that is primary. Other versions are non-primary. Differences between them are:

• Primary versions are started by default when clicking "Start Process" button on process details page.
• Primary versions are shown in progress dashboards for parent processes (for sub-processes and connected instances versions can be shown all).
• Primary versions are suggested by default in "Start Sub Process" actions.
• Primary version can't be deleted from the list of versions. To delete it, you must delete the whole process.

If some non-primary version of process is preferable, you can make it primary (9):

In a 'Add a new process' wizard you can define if duplicates between process versions are allowed or not. When "The process will be used for a single record" checkbox is checked, user will be able to start this process at any record of selected data source object, but only one time at all. If this process is needed to be started on any other record, admin must delete the already started instance of this process.

This article illustrates difference between these two options.