SSD internal HD install

There is no replacement internal drive. But there is this Sandisk SDSSD60:

This picture is roughly life-size (2-in by 4-in), and its about 1/3 inch thick. USB-3 with a trivial USB-C adapter and 6-in cord.

Respectable 500-ish MB/sec read and write. Sizes to 2TB.

Internet Recovery. hold option-command-R at power on and it will try to load recovery from the internet. You'll need an ethernet connection, or if you don't have that a WiFi connection that doesn't need an approval screen. If there's a WiFi password then your Mac will prompt for that. You would need to install MacOS using Internet Recovery.

I assume you have the non-Retina 2012 MBP because the Retina already has a SSD.

The easiest way is to start with the old drive in the computer (I think you skipped this step). Put the new SSD in an external enclosure first and then use something like Carbon Copy Cloner to clone the original hard drive to the SSD. That utility prompts you to create the recovery partition as well so the new drive does everything the old one does. Then remove the old drive from the computer, remove the SSD from its enclosure and put in in the computer and close up.

I did this with my 2012 MBP non-Retina about 18 months ago and the new SSD, once prepared this way, booted first try.

NOTE: On non-Retina 2009-2012 13-inch MBP, it is best practice to change the hard drive cable at the same time you change the hard drives, The cable is cheap, available, and easy to change, especially when you already have the computer apart and the old drive out.

In Disk utility app

Select disk to modify

Select "Partition"

give disk it a name

Select "Journal file system"

Select "Apply"

Sorry for my non-sequitur. That SanDisk drive belongs in a different discussion