How do I enter an account in my chart of accounts for vendor discounts? This is an expense item, right?

Then how do I record the discount when I enter the transaction?

It is a part of the sale, but while making calculation you need to show it on RHS (right hand side), i.e. on debt side separately, and while giving the details to the Sales Tax or GST Department, you will have to subtract it from GTO i.e. the Gross Turnover, and it will not be part of TTO, i.e. the Taxable Turnover.

Yes, it is expenses.

If you have still further query, you are free to ask.