I notice that my laptop has two drives (ie c/: and d/. They are both exactly the same size. Does this mean that I have additional storage space eg can I save stuff to either drive? I haven't touched any of the information/files that are already on d/:
^ as the old saying goes - maybe, mabe not.
You did not indicate which Laptop you have. Normally only laptops larger than 15.6 have daul HDDs some 17" do, some don't If a new Laptop, your "D" drive may be a special partition that holds the "recovery" files.
Easy way to tell if you can use both drives to write to is to right click the drive in my computer, and properties and look at the free space. If you have "Free space" in Both drives then as Hawkey22 indicated - you can use both. If the partitions/drives are set up as "C" = OS + programs and "D" is NOT restore partition, and has the most "free space" Put your files and data on the D drive.