electronics simulation circuit
For a beginner, I have to say Falstad is the easiest circuit sim to get going on. It’s easy to use and it does a really good job of visualizing current and voltage in a running circuit. It has lots of examples that you can easily customize.
Try it here: http://www.falstad.com/circuit/
Two other free Spice sims are LTSpice and Microcap. They’re good, but not as interactive for learners as Falstad.
I don’t much care for CircuitLab. Its UI is kind of buggy in how it handles zoom for example, and it has a weak library.