Nodal Analysis is based on the KCL, and is used to find voltages with respect to a reference node.

The first task is to identify the nodes in the circuit, and for nodal analysis we are only interested in nodes where 3 or more components meet. If we considera ll the nodes it will still work, but we will need more steps.

Then, we pick one of them as a reference node, usually the bottom one

A node is any point where multiple branches connect.