Mentors may use customized sheets. Anyone may use a community sheet. Read all about character sheets in our wiki, and I've excerpted here the section in selecting character sheets: Starting a New Campaign
When starting a new campaign, you have the option to choose the
Character Sheet you want to use from the handy drop-down available on
the New Campaign creation screen. The Character sheet template can be
changed after campaign creation as well. If you're making a Campaign
that's a copy based on an existing Campaign, the copy will keep all
relevant character sheet information to match the original. Finally, you
need to click the (I'm Ready, Create Campaign) button to save.
For an Existing Campaign
To select a character sheet, the GM should navigate to Campaign
Settings (My Campaigns > View Details > Campaign Settings). In the
Character Sheet Template section, select a template from the dropdown.
Mentors can also choose Custom to enter their own HTML and CSS.
Finally, you need to click the (Save Changes) button found at the bottom
of the screen.