you have already inserted the disk now press the power button on and immediately after that hold down the "C" key on loading screen. navigate to the second page of the installation and here you can pull down a menu will appear. Now go to Disk Utilities to format the new drive GUID & Mac OS Extended. Now you can install the system while connecting to internet or by using a media bootable.
Also check the specs on your new SSD drive to see if it backward compatible with the system or not.