Ok lets see;
What distro are you using?
Plug in the adaptor
To enter the commands (please don't do it yet) you will need to open a terminal. It will be konsole or gnome-terminal or xterm.
Open the terminal and log in as root;
enter your root password and press enter;
post the model of the usb adaptor, should have ralink somewhere, you only need to find out what model it is not the whole output of lsusb
another helpfull command is dmesg after you plug in the adaptor