This is probably the hardest part of surfing to nail. It's also the hardest to describe accurately.
When you are learning, it is very difficult to get the 'pop' right. This is partly because the board is flat. As you progress and start taking off in the steeper part of the wave, the process becomes easier, because gravity plays its part.
It is actually worth practicing the 'pop' at home on the floor (although I still have problems doing it here).
To directly answer your question. If your board is long enough for you to push off your feet, then I would do it. If you are watching the majority of surf videos then they are on shortboards and will pop up from their knees.
Unfortunately it is one of those things that only comes with practise. What I would do is go for a 'mid point' of popping up so that your front foot is in place and your back knee is down, then push off your front leg to get off the back knee.
It is hard, but you'll know when you start to get it.
When you've got the hang of this you'll have to try and tackle 'duck diving' which is the absolute hardest thing to get right because you need decent sized waves to practice properly, but that makes it worse when you get it wrong.
Basically, just stick at it and you will get the hang of getting to your feet!