HTML/CSS
One of the most common reasons people learn HTML and CSS is to start a career in web development. But you don’t need to be a web developer to learn these core technologies. As a Web user, there are many great reasons to have the fundamentals under your belt, but here are some reasons why learning HTML and CSS is recommended (Better Understand the Web,Create Websites ,Start a Web Career,Earn Money ,...) to learn it you can start here: https://dash.generalassemb.ly/
JavaScript
JavaScript allows you to build interactive websites. JavaScript has become an essential web technology along with HTML and CSS, as most browsers implement JavaScript. Thus, You must learn JavaScript if you want to get into web development, and you must learn it well if you're planning on being a front-end developer or on using JavaScript for backend development. here you can find some free resources to get started: https://www.codementor.io/learn-javascript-online
PHP
80% of the top 10 million websites use PHP. PHP is particularly popular for freelance work, since many small businesses or non-technical people would want to use WordPress, Wix, or other popular content management systems to set up their websites or shopping carts. PHP was designed for the web, and it does the job well. Facebook has made serious investments into it. This websites contains all what you need to know about PHP:http://www.tizag.com/phpT/
Pyhton
Python is a general-purpose language, which means it can be used to build just about anything, which will be made easy with the right tools/libraries. Professionally, Python is great for backend web development, data analysis, artificial intelligence, and scientific computing. Many developers have also used Python to build productivity tools, games, and desktop apps, so there are plenty of resources to help you learn how to do those as well and this is one of them : https://automatetheboringstuff.com/
Java
Java is a highly portable language as it must be executed through a cross-platform compatible Java Virtual Machine (JVM).Furthermore, Android apps are also developed using Java since the Android Operating System runs on a Java language environment. you can find courses here: http://www.sololearn.com/Course/Java/
C++
C++ is known to be a very powerful language. C++ allows you to have a lot of control as to how you use computer resources, so in the right hands its speed and ability to cheaply use resources should be able to surpass other languages. Thanks to C++'s performance, it is often used to develop game engines, games, and desktop apps. Many AAA title video games are built with C++,so click here to start learning http://www.sololearn.com/Course/CPlusPlus/