Surfing Waves

when you surf do you put your back foot on the tailpad or just infront of it?

Depends on the board, the wave and what you are trying to do. Usually the tail pad is for when you want to turn or lift the nose, so on longer boards your foot is in front when you aren't doing those things (and you move your foot back and forth). However, on short boards your foot has to be on the pad because there is no space/you can't put your weight further forward.

What is a short or longer board in the circumstances depends on your height.

To answer further, I only have pads up to my 6'8 step up, after that none of my boards have a pad because I don't always ride them with my foot over the fins. I tend to rider bigger boards rail to tail, so no stomping on the tail to crank turns, but I do shufflestep my longboard and big wave gun depending on what I need to do with the wave.

So, short boards yes foot on tailpad, not on longer ones

I only have tailpads on my shortboards. Yes, my foot is on the pad. It helps me to feel where my foot is positioned.