Let me recommend a different method.. faster and easier.. unless you are due for a clean install which Tesserax has shown you how to do.
Download and install carbon copy cloner. You can use it free for a month but it is well worth buying IMHO.
Buy a USB to Sata cable. They cost less than $10. I would buy a USB3 one but even USB2 will work.. your 2011 MBP is only USB2.
22Pin-Adapter-Cable-For-2-5-HDD-Hard-Disk-Drive
Here is my actual doing exactly what I described only this is with spinning drive. On a 2011 MBP .. a bit slow but does the job.

Or for longer term buy a dock.
https://eshop.macsales.com/item/NewerTech/U3S3HD/
Then you can create a bootable clone of your Mac onto the SSD.. then test it by simply booting from it.. then you swap hard disks.. the SSD will boot fine when installed if it boots when connected by USB.
Excellent upgrade btw.. I have a 256GB SSD with 8GB ram in the MBP since I bought it.. you will be amazed at the performance improvement.