When it comes to test hypotheses, nothing is more important than p-value. If you have hard time to understand or memorize the use of p-value. Here is a simple way to remember it.
P-value is the probability that the null hypothesis is true. When this value is too small and below a pre-set threshold, we can confidently reject the null hypothesis. This threshold is called the significant level. This value is set by the investigator and normally is 0.05 or 0.01.