There are two ways to open terminal:
To open a terminal window press Ctrl+Alt+T.
Press 'Dash' button at the left top of the screen. Type Terminal in the search bar. A terminal icon will appear. Click on the icon.
After you have opened a terminal window you can type the commands required by your installation guide. Just type required commands (you can even copy and paste) and press 'Enter'.
Some commands require sudo privileges. This means you have to be root (like administrator in 'Windows') to run the command. When you type sudo su you will be asked your password.(the password that you use for installing packages and logging into the desktop). After that you don't have to declare that you're root every time. Type your password and thus you will be able to run as a root.
In the installation process you may be asked to answer Yes or No. As usual you will have to type just Y for yes or N for no.
Other notes are usually stated in the installation guides.