^ is the character for Exponent (EXP on a calculator)
In C you use pow()
In C you can use exponents in two places. Firstly, where numbers are so large or so small that decimal point notation is not human-readable. For instance 100,000,000,000 is best written as 1 * 10 ^11. Secondly where the program logic calls for a value to be raised to the power of another value.
For instance, say you have a virus multiplying in a large population, and each infected person infects another five on average before dying. How many people will be infected after N rounds? The answer is 5^N, or, in C, pow(5.0, N).
For mathematical reasons which are too involved to go into here the expression e^x has special characteristics, so it has its own function, exp(). The expression x^0.5, or sqrt(x) is also special and has its own function – here it is easy for a non-mathematician to see the value of this.