Software is becoming a core part of our lives. Software however needs special skills in order for it to be configured or customized. And in order to be on the cutting edge, a lot of organizations try to maintain customizations to software they use for a number of their core competencies. This leads to software customization or more often customized software development - which done by one or more specialist called the Software Developer.
A Software Developer would write software code in programming languages. You may have heard of programming languages such as Java, C-Sharp (C#), or Ruby, Python, PHP, Swift, or even C and C++. Very often they use application frameworks to write their code on - which provide built-in features which provides them a platform for them to build upon. Examples include J2EE, Spring, .Net, Ruby on Rails, Django etc. So, a developer may come in these various flavours of programming language and application framework they have experience in and can work in.