I don't understand algorithms.Can someone give me a example of a simple algorithm?

An algorithm is simply just a string of calculations that can have numbers inputted at certain locations. Most algebra equations are algorithms. But you are most likely talking about complex algorithms.

Here are some algorithm examples:

Ant colony optimization algorithms, Cooley–Tukey FFT algorithm, Euclidean algorithm, Linear interpolation, and The Stony Brook Algorithm Repository.

A simple algorithm could be:

x = 2
y = 12
algorithm = (x*y)/3
print(algorithm)

As you can see an algorithm can be so simple that we classify it as an algebraic equation.