Kneeling, or seiza, is a formal protocol for beginning and ending class.
The following YouTube provides an understanding of this protocol:
https://www.youtube.com/watch?v=BEYC3TtWycs
We will follow the method that starts 1. sliding the left foot back, kneeling (keeping the back straight), sliding the right foot back, kneeling, spreading the knees and placing the palms on the top of the thighs. 2. rei (bowing): slide both hands at the same time to floor and bring the head towards the hands. 3. standing: go onto the balls of the feet, draw the right foot forward (left knee still down), then stand straight up into misubi-dachi.
But know both methods.
If you have knee problems, a standing bow is OK.