There are two ways to open a terminal window in Linux Mint:
First: you can press the keyboard shortcut Ctrl+Alt+T, and that should work by default regardless of flavor (Cinnamon, Mate, or XFCE).
Second: you can open Cinnamon's start menu and type "terminal." The first result should be called Terminal, and clicking on it opens the terminal.
Note: there are several different terminal applications in Linux systems that call themselves "terminal." You can check which terminal you have by clicking on Help -> About on the terminal window. For example, Linux Mint's Cinnamon comes with GNOME Terminal installed by default, so that is which application "Terminal" is. In Mate, you'll have Mate Terminal. In XFCE, you'll have XFCE Terminal. They all look and work practically the same. I have no idea what compels each desktop environment to have their own terminal.
Tip: many terminals support tabs, and you can open a new terminal tab in the same window through the shortcut Ctrl+Shift+T.
Portability
This same tutorial can work other Linux distros, such as Ubuntu and Fedora.