I used to code by using Notepad++, FileZilla and WordPress’ built in editor. For years. After blowing up one of my sites twice(!) after the failure of built in editor I understood I is not supposed to be so.
Then I did some research and found free Atom. Since then I had only seen it on pictures on agency websites. Took some time for beginner like myself to understand how it works but I love it. It saves so much time and is very much forgiving if I make mistakes.
To get it work through FTP to develop websites you that are hosted on your server you need to install package named Remote FTP, configure the file correctly (instructions are behind the link) and you are ready to go.
For every FTP connection you need separate “folder” where all the files are kept in your computer. If you need to connect no new ftp go File → Open folder (and open just folder).
If you have any questions then there is plenty of information (also about bugs) in Google.