Help with reinstall of El Capitan on my old 2009 MBP.

I was trying to wipe and reinstall El Capitan on my old 2009 MBP. Only to find out after I wiped it that the bootable external HD I had made years ago was no longer operational. Now I can not figure out to make a bootable usb drive to save my life. I have downloaded both an .iso and a .dmg of El Capitan from internet archive, but everytime I try to create the bootable USB in Terminal, I alway get the command not found error. I can not get the MBP to boot into anything other than OS X Utililites and it will only try to reinstall OSX from the internet and I keep getting the 403 error when it tries to verify and download from the Apple store. I feel like I am missing some really simple, yet really important step..... Any options out there or did I jus ​ t brick this laptop?