Welcome to the forum! 
First of all, you have to understand how these things work. GNU/Linux, like all UNIX systems, does not use drive designations. Volumes are always mounted somewhere into the directory tree.
Now, the thing is that if you add some hard disk partition to your existing installation without setting anything up yourself, then the udisks2 subsystem of systemd will treat those volumes as removable storage, and they will then be mounted to a directory under /run somewhere.
The best way to set things up with consistency is to create a static mountpoint for the volume, and to add the information for that mountpoint to /etc/fstab. If you want to use the new volume as an extension to your own home directory, for personal files, then you should create a directory (“folder”) as a mountpoint under your $HOME ─ e.g. /home/your_user_name/Files ─ and to add a line for that in /etc/fstab.
Use lsblk to find out the UUID of the new volume, and then use that in /etc/fstab, like so… 
UUID=some-long-string-here /home/your_user_name/Files ext4 auto,nofail,defaults 0 0
For more information, see…
man 8 mount
man 5 fstab