Create a new game, and specify the type of character sheet you want to use (ie Dungeons and Dragons 5e by Roll20) from the pull down. Go into that game, press the new or plus button and create a character. It will make a sheet with a silly random name. Open that sheet and switch to the character sheet tab and you will get a pop up for the charactermancer. Once you're in the charactermancer it's fairly self-explanatory. You may or may not be able to import the character to a game you join, but you will have an idea beforehand.
