Tax you paid on business purchases can be set against the tax you collect on sales, so you remit only the difference.
This is what makes GST a tax on value added rather than a cumulative tax at every stage. It is also the mechanism with the most conditions attached.
Broadly: you hold a valid tax invoice, you received the goods or services, the supplier has paid and reported the tax, and you claim within the permitted period.
The third condition is the one outside your control, and it is the one that causes the most trouble.
Some categories are blocked, and credit depends on your supplier having filed.
Monthly. The earlier a mismatch is found, the more likely the supplier fixes it.
Yes, in specified circumstances including non-payment to the supplier within a period.
Half an hour with your own data usually saves reading three of these. The guides will still be here afterwards.