It is the computer where a software engineer code or writes test cases.
It typically has following components installed: IDE, build tools, source code management tools such as git
An IDE is a very evolved version of a text editor. And a text editor is a software program that helps you edit the plaintext. It is also used by authors. Please avoid using Windows' Notepad/Wordpad and Mac's TextEdit.
There are many great text editors out there: https://github.com/showcases/text-editors
Some of the text editors such as Vim and Emacs which have good learning curve but it is worth learning to use these text editors.
Back to IDEs. An IDE provides you the following in addition to the ability to edit text:
Examples of IDEs are: