Noobish question - what programming language to learn to edit website?

Hello all, not the smartest question i know but i have to start somewhere.

what the programming language i have to learn to edit my website files? Custom.css, 404.php Etc....

thanks in advance

***PhP, HTML***

Simply start learning HTML and CSS hardly it take 1 - 2 days and if you are ready go for CSS3 and HTML 5 here you will get all you need to edit on designing part for some extend . Then go for PHP and Javascript and it would take some time to learn though and this two will give you idea about the backend of a website .
Use free library like w3school , Code.org , Codeacademy etc

You'll have to learn CSS, HTML and PHP