Q:

How does mapping via Netbios work when the remote host has multiple drives?

Say i want to map a folder on a remote host on my device, for example 
net use Y: \\Server001\Videos 
So far so good, not a problem. But what i dont understand is, what happens if the remote host has multiple drives?
Say it has a C, D and E drive - how does Netbios specify which drive its looking at?

A:

SMB file sharing (not NetBIOS) does not directly deal with drive-based paths in the first place.
Instead, the file server is usually configured to map a share name to a specific path, and it's that mapping which specifies both the drive and the folder. The share name has nothing to do with the folder name at all. (In your case, the share name is "Videos", and it could be located anywhere on the server – it could be "C:\Videos", but it could be "D:\Trash" or "E:\Storage\Movies".)
These assignments can be managed through fsmgmt.msc, or net share, or created through a folder's "Properties" window.

As you discovered, Windows-based SMB servers generally have predefined shares for each drive letter. But these so-called "administrative shares" are only accessible if you have Administrator rights on the server, and might not even be enabled on some OS versions, so you should keep their use to the minimum.
It's better to define custom shares through a folder's "Properties" dialog or through fsmgmt.msc, as then you can select which users to give access to, and you can even move the folder elsewhere without any client noticing.
Note that the $ suffix does not indicate a drive – it only makes the share hidden, i.e. SMB clients usually won't show it in share lists. The shares themselves are not really special.

