Say you go out and you see a sports bar and the FIFA world cup is on. France vs Sweden is playing on the TVs in the bar and the place is packed with fans of both countries. You look at a few people (wearing the national football colours) and you think to yourself "the French fans seem shorter than the Swedish fans". You decide to run an experiment to test this hypothesis. Lucky for you at half-time exactly n fans of each side agree to let you measure their height. You do this and of your sample of n fans, the French are 2cms shorter on average than the Swedish fans.

Now: the p-value is the probability of you getting a result at least this extreme assuming the null hypothesis (that there is no difference in average height between the general population of French and Swedish people).