Right click on directory in rox file manager. Pick open terminal here from the menu provided.
Download this PDF for a manual
Edit: another way
cd /<directory path>
to list what is there
for reading text
cat <text file name>
if need to further dig into another directory where you are at after seeing what directories are showed using ls command.
cd <into deeper territory into the directory you are in>
then cat again to read files in there.