=== EDIT STARTS ===

I am assuming you want it to be mounted every time you boot, if what you want is to mount it one time:

$ sudo mkdir /data-part

$ sudo mount /dev/sdaX /data-part

should do the trick.

=== EDIT ENDS ===

Sure you can. First you need to know device file of the partition you need to mount (it should be something like sda* in most cases). If you don't know, install and run gparted and find out device file of the partition.

Once you find the device file, fire up your favorite editor from terminal (assuming device file you want to mount is /dev/sdaX, replace accordingly):

$ sudo gedit /etc/fstab

When editor opens, go to the bottom of the file and add a line like:

/dev/sdaX /data-part ext4 defaults 0 0

And then, all you need to do is to create a directory at mount point:

$ sudo mkdir /data-part

After your next reboot, partition should be mounted at the mount point automatically.