Radiation exposure is dependent on the inverse square law which states that exposure decreases inversely proportional to the square of the distance. In other words, if you are standing 1 foot away from a radioactive substance and move to 2 feet away you receive ¼ the dose. If you move to 3 feet away you receive 1/9 the dose etc.
You see then that simply moving away from a radioactive source decreases the dose very quickly. Shielding can also be important with heavier and denser substances able to block radiation more effectively. That’s why patients and doctors wear lead shields when x-rays are generated at the hospital.
Nuclear power plants take advantage of both being sited relatively far away from population centers and using heavy concrete and steel buildings which provide shielding as well as containment for safety.