Harmonized Sales Tax, commonly referred to as HST, is a consumer tax resulting from the combination of the Canadian Goods and Services Tax (GST) and provincial sales tax (PST).
As a business owner in any of the provinces that has HST, it's your responsibility to charge, collect and remit Harmonized Sales Tax as required. As with the GST, there is a small supplier exception; if your small business makes less than $30,000 annually, you are not required to register for GST/HST. You may, if you wish, voluntarily apply.
An HST account can be set up simply by you for free.
Visit Revenue Canada's website for HST information and registration.