Help! Error 500 cant log in to admin after playing with editor

Hi there, I deperately need help. I’m only starting to use wordpress for days. So this was what happened:

1) My twentyeleven theme (I’m using a child theme) is not showing sidebar in my posts. So after searching the web every says to edit the Single.php and function.php

2) On my editor for child theme I only have style.css and stylesheet. There wasn’t any single / function php, and I don’t know how to get to my FTP server and what not, so i used a plug in to create a file and named it single.php and copied all the content of the parent theme over and saved it (which was fine) but after I did the same for function.php it took a really long time to save, where I refreshed the page to try and save it again.

3) This is when I can’t log in to my wp-admin or webpage anymore with error:

“Server error
The website encountered an error while retrieving https://myfatpocket.com/justjaslin/. It may be down for maintenance or configured incorrectly.
Here are some suggestions:
Reload this web page later.
HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfil the request.”

4) I tried searching again everyone says about what accessing my wordpress directory / FTP / folder but the problem is I’m an absolute newbie, I don’t know or where to access my wordpress directory. People say to access and edit my folders again through FTP, I don’t know what is FTP, tried searching again they say to use Filezilla (which idk). Ok i downloaded Filezilla software, I don’t know what is my host and I think it needs an account to function. I tried searching again I was told to use cPanel to create an account. Ok I went further and I think you need to pay $ to have a cPanel account or somthing.

So at the end of the day I achieved nothing and please some one help me. I’m only started to use wordpress for a few days and everything is so hard!! I need help!

This is my url btw: www.https://myfatpocket.com/justjaslin/

Thanks in advance.