RAM is the Random Access Memory, the place where the Operating System (OS) puts the open applications and open documents, so working with those is faster.
The HDD is the Hard Disk Drive, the place where you store all your files.
If you are not using more than five applications at a time, and those are not "heavy" (like 3D, CAD, video editing, photo manipulation, compositing, composing music with more than some tracks), HDD should go before RAM.