How do I control the speed on a Triptronic Yaris when doing maneuvers?

I have recently brought a triptronic yaris, It's a perfect car but theres jsut two problems which are cousing major problems for me, 1st is at steepy hills, where the speed suddenly drops, which is rather bad when they are cars are the back of you! and the other main problem is when doing manouvours and reversing, becouse they is no clutch I am unable to control speed - I am driving in 'E' mode which i presume is like 'D' in an auto. How do I conbat this problem without selling my car!!! should I use the other side which is a plus and a minus??? A confused mind!