I have a mid – 2011 Mac computer. I can connect it to the internet. I followed those instructions. After I try to connect it says that I'm missing a file and it cannot download El Capitan.
Try using Terminal.app, located inside the Utilities folder inside the Applications folder. Launch Terminal and at the prompt, type in this code:
softwareupdate --list-full-installers
and press return. It will give you a list of the installers available for your particular Mac. Look at the top of the list and make a note of its version number. It should be the one right after “Versions:” El Capitan should start with 10.11 with possibly another number at the end.
Then enter the command:
sudo softwareupdate --fetch-full-installer --full-installer-version ##.##.#
the number signs replaced by the version number shown in the previous entry. Press return, type in your admin password and press return again. If everything is working right, it should begin downloading the installer app and indicating the progress of the download. Once it’s completed, you should find the macOS installer file inside the Applications folder. First, make a copy of it anywhere outside the Applications folder, for future use, maybe even to a USB thumb drive. Reboot into Safe Mode by restarting and holding down the Shift key. Open the Applications folder and double-click on the installer file and the process should start. Good luck!