The one difference between homo sapiens and other animals is that we are able to imagine things that do not exist. Physicists especially are full of imaginations. First, we imagine electric fields and electric potentials. Then we draw field patterns consisting of field lines and equipotential lines to help us visualize our own imagination.
Just like iron filings can be used to “show” magnetic field lines, grass seeds can be used to “show” electric field lines. Just keep in mind that field lines are not physical objects. They are figments of our imagination.
In practice, we usually map out the equipotential lines first, before we can map out the electric field lines.
Why must electric field lines cut the equipotential lines cut perpendicularly? The video below answers this FAQ.