• Press shift, ctrl and the + sign next to the backspace key at the same time. The cursor should become smaller, and flash near the top of the word it’s next to
• Press 2, and it’ll appear as a squared sign
• To get out of the mode, press shift, ctrl and + again

Additionally, if you want to draw a small number, but at the bottom of a word (In scientific equations, like H₂O), just press ctrl and +, then type in whichever numbers you want…

Hope it’s helpful…