To join the Hereford United Supporters Trust you can fill in the online form on their website - http://www.hufctrust.co.uk/membership-form/ - or complete the downloadable PDF (link) and mail it into their address with payment.
Full Membership costs £10 per year, with the year running from AGM to AGM in September. Junior membership costs £1 and can be registered at the same time as Full members.
Corporate Membership is also available for £50 per year. The membership includes a listing on the HUST website. Please see http://www.hufctrust.co.uk/corporate-membership/ for details.