If you Launch a SmartPath from the SmartPath page, you must choose a group to launch it for. If you only want to launch a SmartPath to one or some contacts, as opposed to a group, you can do this in Contacts or Groups.
Select the check boxes next to the contacts that you want to launch a SmartPath for. Once the contacts you want are selected, click the Bulk Actions button, then Launch SmartPath.
To assign an individual to a SmartPath, click the action pencil icon, then Assign SmartPath.