Trying to create my first invoice, getting stuck

I completed a project ("project A") for a company, the agreed price was $1,000. This is a one-off project and unlikely to repeat. I now want to bill the project and am getting a bit lost as to how to do that. The invoice template seems geared for selling widgets rather than unique projects. For example, I am not sure what to enter for "Units". And I am not sure how I can get GST applied to the $1,000 amount. Any advice or suggestions would be appreciated. Otherwise I suppose I will have to try my accountant next week.

Thanks