How to Transfer files from Kali linux to Android On Android Smartphones

I have installed Kali linux on Android smartphone. I want to transfer files from Android to Kali linux.
and when I am trying to install gmtp (apt-get install gmtp), it is asking password for "SU", what is the default password for SU?

Thanks in Advance

try "changeme"

may i ask to you how u install kali on android step by step and what android device u r using thanks....