The farther away you are from a radiation source, the less exposure you will receive. Compare this to an outdoor concert. If you sit in front of the speaker, you will probably suffer some damage to your hearing. If you sit 50 yards from the stage, you will be exposed to an average amount of music. If you sit in the park across the street, the noise is even further reduced and you might not even hear the concert, or even know what song they are playing.
Radiation exposure is similar.
The closer you are to the source, the greater your chances for developing some damage to your body. If you are far from the source, your exposure would be much lower. For example, if you stand out in the rain without an umbrella, you will get wet. But, if you use an umbrella to shield you from the rain, you will remain dry and protected. This is similar to the idea of shielding in radiation protection.