Where do you configure or what command do I use to mount device at boot? Is it in the file /etc/fstab ?
You need to make an entry in your /etc/fstab for the device that you want to mount at boot. The exact entry depends on the device you are mounting and the options you want to have applied. The format of the file is
<device> <mountpoint> <filesystemtype> <options> <dump> <fsckorder>
A basic example would be
/dev/sda1 /boot ext3 defaults 0 0
This will mount the device known as
sda1 (First partition on the first SCSI subsystem block device) on
/boot using the ext3 filesystem and default options.
A more advanced example is:
UUID=8ade7eb7-dcaf-4e1b-869a-72f3a6f46205 / ext3 relatime,errors=remount-ro 0 1
This will mount the partition/device with the UUID show above as the root filesystem. This is often used with multipath devices. The relatime option modifies how the access time is set on the file.
The manpage on your local system is the best resource for options:
man 5 fstab man 8 mount