Inspiron 7559 HDD, SSD Data Migration

I just purchased a Crucial 8G RAM upgrade and a Samsung EVO 860 1T M.2 SATA  SSD Drive as my Inspiron is slow booting up and it takes forever for Photoshop to load, etc.  I had some work done by a Dell technician to clean some background running apps off, etc., but it's still a little sluggish.  So, I invested in the above.   My questions concern whether all of my apps, documents, pictures, music, downloads and other things on the "C:/" Drive have to be moved to the SSD drive.  Can the "C" Drive still be used for saving these things, or will everything have to be saved to the SSD "D:/" Drive in the future?  Can both these drives be accessed simultaneously.  For example, when I put my SD card into the card slot and want to download my pictures to the laptop, can they be downloaded to the "C" drive and still accessed, or will I have to download them to the "D" drive and then move them from there to an external hard drive, etc.  I have tried to find some answers online, but I am a little concerned.  I am wondering if I should just increase the RAM and send the SSD Drive back to Amazon?  I guess Samsung includes Data Migration software with their piece of hardware.  I would want the laptop to boot up from the SSD and the Apps, i.e., Photoshop, etc., to boot from the SSD, but it would be nice to be able to save stuff to the HDD.  Hope this makes sense.  My  laptop is still under a long-term maintenance / warranty agreement.  I am thinking of taking it to a Dell authorized service dealer and having them help me out with this.  Thanks for listening.