Normally you install the OS on the SSD, and then you install the applications on the SSD. The data files normally go on the HDD. For example, you'd install MS Office itself on the SSD, but the Word ".doc" files and the Excel ".xls" spreadsheets would go into folders on the hard drive.
The way I access the hard drive folders is to create shortcuts to the hard drive folders I typically use and place them into my "My Documents" folder. That way when I use the "File Open" or "File Save" dialogue boxes it's easy for me to navigate my way to the hard drive folders.
A tip: if you put a "$" as the first character of the shortcut names then they'll appear at the top of the "My Documents" folder and they'll be very easy to find.