To start the Terminal you can press Ctrl-Alt-T, or by entering in the search menu the word "terminal", without the quotes of course. You will see this window to enter various commands.
Go to menu - edit - Profile - edit - General tab. In this tab you can change the font. Then go to the tab - Colors. Remove the check mark from the "Use colors from system theme".
you can choose your own color combinations or choose from existing options on the menu - "Built-in schemes". Then go to the Background tab. Adjust the transparency to your taste.
You can create several profiles, which will be changed fonts, transparency, background and text color. Give a name for each profile in the General tab. After that you can change these profiles from the Terminal menu.