The smallest movement is the strongest.
Needless to say (perhaps), the hub is your centre, (your dantien, your core), the spokes are your limbs. When you move your body, this is the part of you that you should feel moving first. As a beginner it’s all too easy to get distracted by what your arms and legs are doing, but actually it’s much easier to do tai chi if you make the centre direct and control all of your movements.
How do you become aware of this? 1) Stand with your feet a shoulders-width apart (not essential, but it helps for a later development of this simple exercise). 2) Turn your hips to left or right, without moving your feet. Then return to neutral. 3) Extend your arm either sideways or ahead of you (with palm turned up or down), and then repeat the body turn. In other words, by turning your body (acting as the hub of the wheel), the arm (acting as one of the spokes) will turn with it.
Pretty obvious, I realise, but the main point is that you were thinking about the turn of the body, and the arm movement came about as a result of that body turn.
The lower limbs. You were standing with your feet a shoulders-width apart for a reason. Leaving the arm out of it for the moment, as you turn the body to, let’s say, the right, turn the toes of the right foot by leaving the heel on the ground and letting the toes pivot around. You are now letting the body control one of the lower limbs as well. Controlling the lower limbs with the hips and waist is the part that even intermediate tai chi practitioners often don’t understand.
Finally. Try shifting you weight on to the foot that you are turning out. Don’t wait until you’ve turned it out and then shift it, move the weight on to the foot as you turn it. As the weight transfers, the other foot will also need to move, otherwise it will feel twisted. So, as you place the right foot in its new position, let the left foot turn also, either 1) by pivoting on the left heel so that the left toes turn, or alternatively 2) by keeping the left toes on the floor and allowing the left heel to push backwards (i.e. you are pivoting on the toes). Either is okay.
Now you are doing a tai chi move with the centre leading the movement of the lower limbs.