You can open a Terminal window by selecting the Applications menu, then Accessories, then Terminal. You can also open a new terminal window from an existing one by choosing "Open Terminal" from the File menu or by pressing Ctrl-Shift-N.
Lastly, you can type gnome-terminal & at your shell prompt.
You can also use the "xterm" program, which is an older, but in some cases more customizable, terminal window. To get a new xterm, simply type xterm & at your shell prompt.