How to move one file to a folder using terminal?

mv [filename] [foldername]
so to move info.txt into the config/ folder, type mv info.txt config/
~~edit~~
As was pointed out in a correct comment, the above will fail if the use running the command doesn't have write access to either the file or the folder.
use sudo to tell the system to run the command as the root user (similar to an Admin account) . IE sudo mv info.txt config/.
BIG IMPORTANT NOTE: Only use sudo if you are sure you know what you're doing - Ubuntu protects things for a reason. Using sudo you can break you OS, forcing a reinstall, if you move (or delete or whatever) important files.