Statistical Applets: P-Value For A Test Of One Proportion
This applet illustrates the P-value for a significance test involving one population proportion, p. These concepts easily apply to any other significance test for the center of a distribution.
The Normal curve shows the sampling distribution of the sample proportion p̂ when the null hypothesis is true. The blue arrow shows in which direction the "extreme" values of p̂ will be evidence against the null hypothesis, H0 in favor of Ha.
If you change the alternate for any situation, you can see the impact on the P-value (the probability of a sample result at least as far away from the null value as that seen in the data, assuming the null hypothesis is true).