On your AndroidOS device

  Install Termux (https://termux.com/)

  Launch Termux

  Type these commands 

     > apt install openssh

     > touch ~/.ssh/authorized_keys 

     > chmod 600 ~/.ssh/authorized_keys

     > chmod 700 ~/.ssh

     > ssh-keygen

     > cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

     > chmod 600 ~/.ssh/authorized_keys

     > sshd

     > scp ~/.ssh/id_rsa [email protected]:/path/of/id_rsa

To SSH into Android from the Remote Host

   Type this command from within a Terminal

      > ssh -p 8022 -i /path/of/id_rsa IPofYourAndroid 

To SFTP into Android from the Remote Host

    Type this command from within a Terminal

      > sftp -P 8022 -i /path/of/id_rsa IPofYourAndroid  

     

   Make sure you have SSHFS installed 

   Type this command

      >sshfs anything@IPofYourAndroid:/data/data/com.termux/files/home/ /path/on/remote/to/mount/ -p 8022 -o IdentityFile=/path/of/id_rsa

   Once Mounted you can access the files and directoris on the Android device from 

   any app/program (example, file managers, Atom editor, Libre Office, etc etc)

SSH Under Termux - https://oliverse.ch/tech/2015/11/06/run-an-ssh-server-on-your-android-with-termux.html

Termux Help - https://termux.com/help.html