Short answer: Once ready, final files can be shared through your Commissions > Final Delivery tab. Before then, please communicate via VGen Direct Messaging for regular updates.
Please prioritize reaching your clients via VGen DMs, however if you're unable to reach them there, feel free to communicate with them via Discord, Twitter DMs, email, etc. as well.
Final files can be shared through the Final Delivery tab of your commission. When you've submitted your Final Delivery, your client will get notified and they'll then be able to download their files and submit their review.