Hi Alex,
I recommend you read the FAQs and take the Tutorials at HELP (link at top of page) to get you started. I'd also review all of your account settings and make sure they are appropriate to how you want to operate, especially using the default Auctiva Insurance plan and Auctiva Checkout.
You build listings with Auctiva's one-page lister, similar to eBay's one-page lister. You can find that at the LISTINGS tab. Once the listing is ready, you can either submit it immediately or use Auctiva's free scheduler for submission and Auctiva will send it to eBay for you.
Hope that helps and welcome to the Community.
Danno