User @Jos gave already a good answer in his comment.
Just to clarify it further: it's true that Ubuntu has somewhat different partitioning model than Windows and thus doesn't use letters for partitions.
But you can freely place additional partitions (mount it) under /media/ directory - but of course, please reserve at least one partition for the Ubuntu needs (or alternatively two):
- one for Ubuntu itself under
/ - equivalent of C: in Win (20 or 30 GB would be enough)
- and the second for users directories
/home - equivalent of D: (let's say 200 GB).
All remaining partitions you can place under /media/ directory. Sth like:
/media/e
/media/f
/media/g
You can do it during the installation by choosing Something else, or even later, after the installation, with the mentioned GParted program.
gpartedscreen where you can create these partitions the way you want. – Jos Jun 18 '18 at 07:32