Add an entry to /etc/fstab. This is only necessary if you want to establish a persistent association between the device and a mountpoint. Use the decrypted device, /dev/mapper/<name> in the /etc/fstab file.
In many cases it is desirable to list devices in /etc/fstab by UUID or by a filesystem label. The main purpose of this is to provide a constant identifier in the event that the device name (eg: /dev/sda4) changes. LUKS device names in the form of /dev/mapper/luks-<luks_uuid> are based only on the device's LUKS UUID, and are therefore guaranteed to remain constant. This fact makes them suitable for use in /etc/fstab.
For details on the format of the /etc/fstab file, read the fstab(5) man page.