If you are a GST compliant company and want to claim Input Tax Credit (ITC) for the bill, you can select the check box and the GST amount for the bill will be added to you ITC form.
More on GST ITC: The GST that you incur on business purchases and expenses (including import of goods) is known as input tax. Input Tax Credit or ITC is the tax that a business pays on a purchase. It can be used to reduce its tax liability when the business makes a sale. In other words, businesses can reduce their tax liability by claiming credit to the extent of GST paid on purchases.