You didn't specify this, but I'm assuming you are Canadian.
You'd only charge GST to Canadian customers of yours. It would be HST depending on where you live, and where your customer lives. Just about all Canadian companies will pay the GST you add with no questions asked. Just make sure you present them with proper invoices that include the pre-tax, tax and after-tax amounts and that the invoice contains your full company name and GST number.
You'll need to submit the GST you collect quarterly, or monthly, to the government depending on the thresholds you hit. You can submit the GST through most banks on-line systems. You'd probably need to get setup with your bank for this.
You'd also have to keep track of all GST you pay to suppliers and subtract that from the GST you collect before you remit to the government.
If you are using a professional accounting software package (such as Quickbooks), management of GST is pretty simple.
