In Windows, any disk partition gets its own drive letter, whether it's a different physical device, or if it's merely a partition on the same device. Windows is stupid like that.
Linux improves on the process by giving you a way to tell the two apart. When you attach a physical hard drive, it'll be recognized as /dev/sda. A second one would become /dev/sdb. And so on.
Each partition on each device would get a partition number. So the first partition on /dev/sda would be /dev/sda1, then /dev/sda2, /dev/sda3, etc. The same pattern applies when you format and then partition /dev/sdb.
Once you've completed the process of formatting/partitioning your disks, you then mount them. Each partition is a filesystem, and each filesystem gets mounted somewhere along the directory tree. You pick where.
The top-level directory is root (/), and /dev/sda1 will always mount there. Typically, /dev/sda2 is your swap filesystem, so you won't go browsing that, since it's a different filesystem type altogether. The next one to mount would be /dev/sda3. You'll pick a mount point somewhere along the directory tree (someplace empty, or else you'll end up making the files under it inaccessible... sometimes that's a good idea, usually it's not what you want, though). When you want to do an ls -l of that filesystem, you do it to the mount point.
For example, if we mount /dev/sda3 at /var, then the way to browse the contents of /dev/sda3 would be: