How to access the USB and TF Card Storage in Android 6.0?

You can find the External TF card and USB Storage in the/mnt/media_rw directory. 

You can also refer to the demo that explains how to access them here:

https://github.com/leavs/WRFileDemo.git

Check https://github.com/leavs/WRFileDemo.git to learn how to use them.

For the signatures Tools, please download them from the following link:

https://chipsee-tmp.s3.amazonaws.com/Tools/imx6_android6.0_security.zip