Ok... Let me try to clarify a bit. This is one of the hardest concepts that long term Windows users have to unlearn when they come to Linux/Unix, so don't feel bad. You have to stop thinking in terms of C drive, D drive, etc.
Everything in Linux is part of "the" file system. / (root) and the folders in it, constitutes the entire system. The folders in Linux/Unix have evolved over time, (Unix was around when Bill Gates was still using a nipple), and by convention each folder has a specific use. For example; /user contains all the program binaries that the users use. /boot contains all the files needed to boot the system and the Linux kernel. /var is the area that is used as a temporary work and holding area for the kernel. /home is where all the users of the system store their individual configuration files and store their data. Remember Linux/Unix was designed as a multiuser system. That's not all of the folders of course, but that gives you an idea of what I am talking about.
This file system is not tied to any storage media until it is "mounted." The entire file system, (/ (root) remember?), can be mounted to one local hard drive or split up over several hard drives or even several machines all over the network. This method gives a tremendous amount of flexibility to the organization of the system.
You can mount a drive partition to any of the folders in the file system. Not only to the main folders of the default system but also to any folder that is in the system. Even folders you create.
Now to your questions.
1) /home is the folder that all the users of the system use for their personal stuff. So if you look in /home you would find a folder for each user. Fred, Denise, Sarah, Catherine, Amy; as an example. If you open one of those folders you would find configuration files for their desktop, their data folders; pictures, documents, etc. Any folder can be mounted to a partition. So you could have a separate partition for each type of date if you wish to. Linux only sees the file system. After partitions are mounted to folders, it makes no difference what combinations of drives and partitions are being used.
2) Yes "/home/your_username/My_Data" would be a mount point in the file system, If you have created a folder in your /home/fred directory called "My_Data. Of course you can call that folder you create anything you wish as long as you mount it that way.
3) Linux does not see drives or partitions. It only sees the file system. You can construct and tie that file system either in whole or in part to any storage you wish, within reason. It can be made as simple or as complicated as your needs and desires require.
The advantage I was trying to give you with the way I showed you was to keep your personal data independent of your operating system. The way I showed you, you could destroy your system and still have your data intact on its own separate partition or partitions, as the case may be.
I hope this helps you.
EDIT: If you want to see what my main set-up looks like, you can look at the thread below. Different from what I was suggesting, but I have different needs. Just shows what flexibility Linux has.viewtopic.php?f=46&t=10043&start=30