dolphin software package provides file manager, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install dolphin
dolphin is installed in your system.
Make ensure the dolphin package were installed using the commands given below,
$ sudo dpkg-query -l | grep dolphin *
You will get with dolphin package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Utilities |
| Package | dolphin |
| Version | 4:16.08.2-1 |
| Description | file manager |
| Sub Section | Utils |