set your account info
http://www.auctiva.com/account/landing.aspx
Note: if you have an authorize.net acct, post in forums for help with it. it's fairly straighforward, but at same time can be frustrating if you arent aware of the various things that you have to do
The Store Tab
your Auctiva store is not a store, per say. it's a gallery of items of yours for sale. There's the store window, which is in listings and shows a preview of various items, and there's your auctiva store page which is a webpage with overview of items for sale
At the store tab you can turn window off and on, prevent specific items from appearing in store window, set colors of store window, etc.
The Profiles Tab
here you can set various preferences that you use frequently. much faster to do listings if you set up profiles, cause can then create a new listing, select a profile, and most of the info is configured. There are Profiles and Master Profiles. Types of sub-Profiles are Shipping Profile, an Item Details Profile, a Marketing Tools Profile, and a Checkout Profile. A Master Profile is a Profile with a select group of those subprofiles. Ie: if you have shipping profiles name ship1 and ship2, and Item Details Profiles named type1 and type2, you can do a Master Profile that has ship2 and type1 select, another one that has ship1 and type2 selected, etc.
Images Tab
Where you manage your images (upload them, rename them, sort and organize them, etc)
Listings Tab
Where you create and edit listings and templates
If you've never create a template before, I recommend using some of the prebuilt templates for starters.
That's the basic rundown of what's where. and I would start at the top of the list and work your way down. (configure acct, configure profiles, etc and then do a listing)
I know that's not a very complete guide, but hopefully it'll point you in the right direction of where to start, etc.