How can I put GST on my purchases column?

Hi there, 

Welcome to the Community. QuickBooks offers a powerful tax module that helps you streamline your work with ease. I'll be happy to guide you in the right direction. 

Here's how to set up and use GST:

1. Go to Taxes and select Set up GST.
2. Select Start of tax period and Filing frequency from the dropdown.
3. Select your Reporting method (usually it'll be Accrual, but if in doubt, please consult your accountant).
4. Enter your Business ID No.
5. Select Next, then select OK.

For more info, check out the following article with more info on how to: Set up and use GST in QuickBooks Online. 

Let me know if this info helps. I'll be a message away in case you have other questions.