Good. You're nearly home free. Obviously it's absolutely crucial that your source disk be problem-free since if you clone garbage, garbage is what you get.
So, since you're working with a desktop PC it's a virtual certainty you can internally install your SSD in the system. Once you've accomplished that you'll need a disk-cloning (data migration) program to effect the transfer of the total contents of the HDD to the SSD. (The HDD's contents will, in effect, be copied over to the destination drive, not moved.)
There are a number of freely available disk-cloning programs available on the net; one of the more popular ones is the Macrium Reflect Free program which you can download from...http://www.macrium.com/reflectfree.aspx
Following the successful disk-cloning operation, it would be wise to reconnect the SSD to the motherboard's first SATA data connector - generally designated SATA0 or SATA1. That data connector will probably be the same one your present HDD is connected to. You can then connect the HDD to the following SATA data connector.
But first disconnect the HDD from the system and boot to the SSD with no other connected disks. Ensure the cloned SSD boots & functions without any problems. Do check your BIOS (or UEFI interface) to ensure that the SSD is first in boot priority order. Then reconnect your HDD after shutting down and boot the system to determine all is well.
DO NOT make any wholesale changes/deletions to your HDD for some days until you're satisfied the SSD is properly functioning in all respects.
Good luck.