I am learning web development using django ..can i use same database or i have to write a new one for app? how do i merge?

1..I am learning python and web development using django(framework of python for web development). I wanted to ask if i can connect the database (backend code written in django)of my website to my app also?

2..or can i convert my whole website to app using some tools?

3.. I have learnt that to make an app , you neccesarily need to learn java and write code in java in android studio . And does that mean I cant design my website in Django?? because i have to maintain both my website and app (and if database is same , it would be a bonus).

4...instagram code was written in python(backend and database) ,so how the instagram app is running? do they have written a separate code in java for their app,and database or they have somehow connected the django database with app....

any help is highly appreciated.

If i am wrong with something, suggestions are most welcome