Short answer: Once ready, final files can be shared through your Commissions > Final Delivery tab. Before then, please communicate off-platform for regular updates (on-platform DMs coming soon).
Before DMs are available on VGen, feel free to communicate with your clients via Discord, Twitter DMs, email, etc.
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.