Ask HN: How do I share the code with interns or freelancers for ongoing project?

I'm trying to build a bookkeeping software, we have a developer working part-time, on weekends mostly for past 6 months but the progress seems to be really slow, so I'm looking to hire an intern or freelancer to speeden up the process but I don't really have an idea how much of the code to share.Would appreciate any advice and suggestions. https://vaporinterface.com/