To onboard team members to start using Asana I can recommend going through How to get your team started with Asana in less than 5 seconds - The Asana Blog
There is an onboarding checklist project that you can download also from this site.
Here are some courses for your team to get to know the basics https://academy.asana.com/page/get-to-know-the-basics
And once the basics are covered I’d recommend you definitely should create some short tutorial videos about your individual project set-up
And here was a discussion as well about this topic