Here's what to do when you get the SSD, BEFORE you open up the MacBook:
Get an external 2.5" enclosure like this:
SABRENT 2.5 Inch SATA to USB 3.0 Tool Free External Hard Drive Enclosure [Optimized for SSD, Support UASP SATA III] Black (EC-UASP)
www.amazon.com
Only $9.
Put the SSD into it and connect it to the MacBook (with the old drive still inside and running).
Open disk utility and erase the SSD to "Mac OS extended with journaling enabled", GUID partition format.
Now, download CarbonCopyCloner from here:
www.bombich.com
CCC is FREE to use for 30 days -- this costs you nothing.
Use CCC to "clone" the contents of the old internal drive to the SSD.
It will take a little while to copy everything over.
Now, TEST the SSD BEFORE you open the MacBook.
Reboot and hold down the option key CONTINUOUSLY until the startup manager appears.
Does the SSD show up as a bootable choice?
Then... select it with the point and hit return.
You should boot from the SSD in the external enclosure.
Do you get "a good boot"? (It will look EXACTLY like the old drive when you get to the desktop, because "it's a clone").
If so, NOW is the time to shut everything down and "do the drive swap".
BE SURE YOU USE THE RIGHT TOOLS FOR THE JOB.
Go to ifixit.com to see what's involved for your particular MacBook.
When done, if you get a good boot with the SSD now inside the MacBook, take the old drive and put it into the USB enclosure. It can now serve as your backup drive.