The reasons can be:

• Insufficient privileges - you must have system administration permissions to activate a process. Please ask someone with system administration rights to activate it for you.
• Unauthorized endpoint error - you need to set the Remote Site Settings for this organization.

You should add the Work-Relay Progress Component to your object record layout.

Make sure you Activated your Process in the Process Builder in Actions menu, or when saving.

For a process to show up as a sub-process:

• Start Type must be "Triggered by another flow".
• The process must be activated.