Unless I've mis-understood your query (my apologies if this is the case), when site's load, the tabs should be in the window tabs bar (View > Toolbars > Window Tabs), unless the window is closed (e.g. by clicking the X).
Holding Shift when clicking a link will open the content in a new tab. You can also configure AB to open certain things in new tabs by default. See Tools > Avant Browser Options > New Window and look under Always create a new window for:
jozza50 wrote:how can i keep the browser windows open so i can change fron site to site quickly.