the back and forward buttons are in the top left corner, though you only see them when it makes sense. IE, unless you have a page to go forward or back to, you will not see any arrows. If you go forward one page, you can see a back arrow and if you press it, you can see a forward arrow..and if you've gone to 3 sites the middle site will have both.

As for tabs, you can open a new tab and each tab is it's own "card" or window.. so you will see them each on the multi-task screen but atm (at least on my phone) there is no actual "tab" to switch between when you are looking at one window of the built-in browser

EDIT bleh corrected my erroneous answer