University of Alberta Guide/STAT/222/Formulas and Functions:Cumulative Distribution Functions

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The $F_X(x)\to (cdf)$, represents the probability that the value of a random variable $X$, regardless of its distribution, will be less than or equal to the value $x$ that is provided. For continuous random variables, $F_X(0)=0$ because $P(X=0)=0$ for all continuous random variables. Therefore, all cumulative distribution functions will start at zero.
Generally, $F_X(x)$ represents $P(X\le x)$, however, if what is desired is $P(X>x)$ then $1-F_X(x)$ would be used.

CDF for an Exponential RV

Notice that as $x$ increases, the probability nears closer and closer to one. This is because as $x$ increases, the area under the curve of the PDF becomes closer and closer to one.