You cannot send client passwords via email, since this is not optimal from a security point of view. You can, however, send the username and a password reset link to your client from CONTACTS TAB > CONTACT NAME > "Profile" tab > Client Information section > link "Send reset password link to client." This sends the client a message that uses the template found in My Account > Notification Templates > Password Reminder. The replacement tag $PASSWORD$ used in this template (and anywhere in your communications to the clients) will generate a custom link for the clients to (re)set their password.
Your client can change their own password by logging into their private client website > "Profile" section under the FORMS tab > scroll down to the Password section.
If they forgot their password, and can't login to their private client website, they can use the "forgot password" link on the client login page and follow the instructions for password recovery.