Why is not esay to ride bi cycle if the tires pressure is not OK

With the tire pressure low the rubber on the tire moves from side to side making steering harder.

Also more of the tire is hitting the surface of the ground causing more friction.

When there is more friction it takes more energy to move the bike and peddling the bike is harder.

Be very careful if you pump the bike tire at a gas station. It's a very small tire and the air pressure builds up quick in it and it can blow out the tire quickly. Put short burst of air in it and check the pressure with a tire gage as you pump it up.