The activation function plays a crucial role in determining whether a neuron should be activated based on the weighted sum of its inputs together with the addition of a bias. Its main function is to introduce non linearity into the output of the neuron, allowing for more complex and adaptive behaviour of the neural network.
"The activation function decides whether a neuron should be activated or not by calculating the weighted sum and further adding bias to it. The purpose of the activation function is to introduce non-linearity into the output of a neuron."