Blocks are great a prop and has many uses. Here are are few examples of how they can be used below.
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FORWARD FOLD. Try this, for more comfort in the lower back.
PIGEON POSE. A block under the buttock will create ease in the pose and for the knees.
TRIANGLE. One of the best. The block will help you explore various positions and maintain alignment of the body.
STANDNG FORWARD BEND. Always soften the knees and for comfort use the block. Breathe easy.
BALANCE. Try this one and see how the block helps to stabilise you in single leg flying balance pose.