This is a good resource:
Statistical power - Wikipedia, the free encyclopedia
Think about power is the ability to handle the situation when H0 is rejected when it should be.
In hypothesis testing you have two errors and the other scenario when you accept the right hypothesis.
A test with good statistical power will reject H0 when it needs to be rejected with higher probability and minimize those other errors.
You can never get rid of the errors, but you can do your best to minimize them in the best way possible both with statistical theory and with practical techniques that involve sampling protocols as well as experimental design and survey analyses.