Continuous distributions are constructed from continuous random variables which take values at every point over a given interval and are usually generated from experiments in which things are “measured” as opposed to “counted”.
With continuous distributions, probabilities of outcomes occurring between particular points are determined by calculating the area under the probability density function (pdf) curve between those points. In addition, the entire area under the whole curve is equal to 1.
The following video explains probability density functions for continuous random variables.
The following video gives a brief discussion on probability density functions and continuous random variables.
The following video shows how to calculate probabilities from density functions.