This movement involves moving forward as well as up, so it is easiest to imagine a trajectory of about 45 degree angle as you get up.
One starts with one knee and toes on the ground, the other foot forward and on the ground. Bring the pelvis forward so your body-weight is over the forward foot, then push down through the floor with the forward leg, and push the body forward with the back toes to stand up. The work should be felt in the buttocks and upper hamstrings of the front leg.
It can be helpful to have a walking pole, or even pretend to use a walking pole in the opposite hand to the forward leg. As energy is exerted by the forward leg to stand up, the opposite arm is pushing down and back through the pole (or imaginary one).
Getting up from the ground in this manner is one of those basic movements that everyone should always be able to do easily with both legs. This movement would also ensure the ability to step up onto a high step or rock, or step over a small fence.
The movement can be made easier by putting a step or small platform under the back knee, and can be made harder by putting a step or small platform under the front foot.