GST stands for Goods and Services Tax.
The GST is "a 5% tax on the supply of most goods and services in Canada" (Canada Revenue Agency).
As a consumer, you pay the GST on all taxable goods and services, except zero-rated and exempt goods and services; as a business, you charge GST on all taxable goods and services.
There are always exceptions. Provincial and territorial governments and Aboriginal people do not always have to pay GST; businesses that are deemed to be Small Suppliers by the Canada Revenue Agency (CRA) do not have to charge GST.
A GST Small Supplier is defined as a sole proprietor, partnership or corporation whose total taxable revenues before expenses are $30,000 or less in the last four consecutive calendar quarters or a public service body (such as a non-profit organization) that has total taxable revenues of $50,000 or less in the last four consecutive calendar quarters.
Some businesses, however, are not allowed to claim Small Supplier status; taxi and limousine operators, for instance, must register for GST/HST no matter how small their annual income.
If you do not qualify as a Small Supplier and provide taxable goods or services, you will need to charge, collect and remit the Goods and Services Tax. The basic process is to register for a GST/HST account with the Canada Revenue Agency, keep track of the GST/HST that you collect and/or pay, and complete and file a GST/HST tax form every quarter.
You can claim an Input Tax Credit (ITC) for the GST/HST that you pay or owe "on purchases and expenses you use, consume, or supply in your commercial activities" (CRA).