Help needed to get Mac Book Pro running again!

If your Time Machine backup is a full system, then use OPTION boot and select the Time Machine disk icon from which to boot. Once in the Recovery HD you can partition and erase the new SSD, then restore the rest of your Time Machine backup.

Or, see: Computers that can be upgraded to use OS X Internet Recovery. If your model qualifies or can be updated to use Network Recovery:

First, you need to remove the old drive and install the new SSD.

Install OS X Using Network Recovery

Be sure you have backed up your files because the following procedure will remove everything from the hard drive.

Boot to the Network Recovery Server:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the out-dented entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Apply button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

You should be able to install El Capitan on the SSD. Mountain Lion is no longer available for download.