Clivern

These technologies complete each other, so django is just a framework to build web applications rather than writing everything from scratch in python. there is other frameworks too like flask or AIOHTTP.

PostgreSQL is a relational database because you will probably need to store the data in any datastore either relational or non relational. There is also mysql that is quite similar to PostgreSQL.

I would say it is quite popular to use django with MySQL or PostgreSQL for python developers but this may change based on what your are building. maybe you will need other frameworks or other datastores like redis, Message Broker or non relational database like mongodb.