Django is a web application framework written in python. It is used to create dynamic database driven web applications. It is used by a large number of developers because it is easy to use, takes care of a lot of boilerplate code related to common web application development tasks such as user authentication database access, dynamic templates etc.
If you wish to learn more about Django you can take this end to end Django certification course.
If you just wish to get your feet wet and try dajngo out you can follow this Django tutorial.