Our human brain has millions of neurons that talk and transfer signals to each other. So, when one neuron calculates a signal and transfers it to another neuron, the second neuron that is connected to the first neuron becomes their input and acts on it. In this way, the initial input goes through various neurons while being altered at each level until a final deduction can be made. You can think of our brain as a graph of these neurons interconnected to each other, and sending signal or inputs to each other.
Let's see how a typical neuron in the human brain looks:
This picture of a human neuron has been taken from Wikipedia and can be seen at this link: https://en.wikipedia.org/wiki/Dendrite. The neuron has some important components, as seen in the labels in the image. They are explained as follows: