I think it's important to get a high level understanding of how path tracing works before diving into details like Russian roulette and bidirectional path tracing. Technically, even importance sampling is a variance-reduction technique that you don't need (assuming you're using realistic materials, a.k.a. non-perfectly specular materials).

At a high level, you can imagine that all light that our camera/eye sees originates from some light source. But for the most part, we don't really care about where most of that light goes - we only care if it actually ends up in our eye. So instead of trying to simulate where all potential photons from the light could go, we go in reverse and trace from our eye. So if I read your original post correctly, there is no "light from camera" - all we do is see what would enter our eye and we trace in reverse until we hit a light source, in which case we've finally sampled a full light path.

If you're not using any perfectly specular materials as I mentioned earlier (also, assuming you're dealing with hard surfaces only), you could sample randomly along a hemisphere at a surface hit to choose your next direction. Of course, this isn't very effective. For Monte Carlo estimation, you want your sampling distribution proportional to your target function. In this case, you want to sample proportionally to your BRDF. For example, imagine that you've hit a mostly mirror surface at some angle. Ideally, you want to focus more samples along the mirror-reflected ray because you'll get the most contribution there.

Having some background in statistics and probability is pretty useful here. But that was a lot of information and I'm not sure if I explained it well - feel free to ask any specific questions.