There isn't much to it: Font Mate shows you a list of all the fonts installed on your computer. Choose any font from the list and it will show you what all the characters in that font look like.

Choose any one of those characters and you will see an enlarged version of it at the bottom of the page (with its ASCII code in decimal and hex, should you be interested).

You can copy any character to the clipboard. You will also see some sample text (a random pangram plus numbers) but you can write your own if you prefer.