best and original as Buddha yes you should sit But not necessary of you are new. sit down require a fitness strenght to be able to sit and have a good posture. also if you are well train your mind then anywhere you can work and meditate all about your focus on your inner peace.
No , it's not necessary to sit down to meditate. You can be walking,lying down in bed or doing any other work, you can meditate.
But you need practise in order to be able to do it in different situation. It's easy to start by sitting in a meditation space at your home with some music and candle lights.
Just observe your breathe going in and out. Just be in the moment. If your awareness drifts away bring it back.
You can do it anywhere and anytime.
No, there are different forms or kinds of meditations. There are even walking meditations. I suggest you experiment with which meditations are most relaxing and beneficial for you. Yoga is considered to be a moving meditation. Meditation is a single minded focus. I personally get into my deepest state of relaxation and calm if I meditate laying down (I personally very rarely fall asleep unless I'm really sleep deprived in which case I probably need sleep). I like meditating while laying down because as a 20 plus year meditator I came to discover that it takes subtle energy to even sit and I can continue to hold tension and it is most rejuvenating to give the whole body a break if you can.