Hello,
you can also see here: Social
to understand how to "find" the file that you want to send, I mean the directory.
This is what I saw and did that in the picture:
To help you understand... I have a folder called "apt" in my files and I want to send the file "ind_users.txt" which is IN THE folder "apt".
And the idea of "join" that somebody has told you is this.
I hope you' re fine!