You need to copy .env.dist and rename it as you want, removing *.dist suffix.
Every *.env file represents a project, for example you can have "my-personal-site.env".
You can have as many .env file as you need, once for project.
Fill all the parameters inside the file before start dumping.
DUMP_DIR is the directory where you need to put database backups
$ cd docker-import-database
$ bash restore-db.sh
Then write inside the bash the env name you want to use without .env extension like this:
...
Tell me .env name and press [ENTER]:
my-personal-site
-----------------------------------------------------
Using my-personal-site.env
...
If you did right, you only need to choose from a list the database dump you want to import