This will be a rather broad answer since the question was not specific.
Here is the definition of a software developer from Wikipedia: Software developer
It will really depend on the company that you work for. In a large company you might be developing software for a very specific piece of functionality, but at a smaller company you might be involved in software design, testing, deployment, changing database schema, etc.
For the most part you will work with a set of requirements and follow either an Agile or Waterfall process for development. It involves working closely with other engineers and the product/project owner to make sure your code meets the requirements. It will involve working with source control systems like Git and following your companies software design standards.
It might also involve fixing bugs and checking other programmers code.
Source: Quora