If your clothes come out of the washing machine feeling stiff then it's usually caused by hard water in your area and the detergent.
When you have hard water and wash clothes you usually need to use more detergent than you normally would.
If not enough detergent is used, there can be insufficient active ingredients to combat the hardness of the water, which in turn can affect the softness of the fibers in the clothing which leads to the clothes feeling stiff.
So you may need to get rid of the hardness of the water or use some more detergent.
After the wash cycle you may need to add some fabric softener to the washing machine to help with the stiffness of the clothes.
Sometimes adding some baking soda along with your detergent during the wash cycle can also help with the clothes becoming softer when they normally come out stiff.