A "Set Password" function is available to set a specific password for a customer. This may not be suitable for all installations because it means that the Administrator gets to see the customer's password. For this reason this functionality isn't enabled by default. If you want this feature to be enabled add the "Set Password" panel to the appropriate role.

The password (which can be generated automatically by clicking on the "Generate" button) is not sent by email to the customer so would need to be communicated to the customer in other ways.