checkout issue

hi,

recently i just add payment method in my shopping cart...unfortunately there are some problems with the checkout progress...when i click next at the last step, it will goes to the payment method...problem is when i click to back button, i can't go back to previous page..can u guys see what is the problem actually...

2nd thing is how can i set email function so that client will get their notification email after they confirm purchasing the product cause at this time, client will get email notification after they click 'next' button and goes to the payment method...

hope u guys can help me to solve this thing because im not good enough in programming.. this is the link for u guys to test...

medi-life.com.my/ecart/