Earlier today, attempted to explain what tense and mood "look" like to me while studying French. But I think a couple of commenters have done a much better job at bringing the abstract to life.
Here is an especially mind-blowing way to think about it: Tenses provide ways of talking about temporally distant locales in this spatiotemporal volume -- points in the past, present, or future. But subjunctive constructions provide ways of talking about potentially counterfactual realities -- about points in a space that includes spatiotemporal volumes that are utterly disconnected from this one. Call these "alternative realities" or "possible situations."
If this is your visualization of French tenses, a way to helpfully extend that to include the conditional might be to think of these other things not as intersecting lines but as complementing or parallel lines. Imagine you've got a line drawn on a page. Now imagine you realize that that line is actually more like a plank or a rectangle--it's got width to it. You still move between past, present, and future linearly, like you did before. But now you've got the ability to move sideways within this broader line to express different attitudes about past, present, and future.So "Je voudrais un café" sits right in the same general area that "J'ai besoin d'un café" does--it's next to the present tense on your mental timeline. But rather than being a dot on that line, it's more like a region of coverage. It extends a little bit into the future. And it also gets in a little bit of your attitude about the wanting--it's conditional. It's couched. It's not a direct line from wanting to having. It allows for other circumstances, the whims of other people.Or take a sentence like "Il serait ici s'il n'était pas malade" (he would be here if he weren't sick). Serait is a future conditional, formed by adding the conditional ending onto the regular future tense of etre. So on your mental timeline, it sits next to the future tense. But it expresses something more than a simple statement of future. It's a would-be, could-be future. It's a broad future with coverage that almost reaches back and touches the present because in an alternate universe, where he isn't sick, it IS the present.
You're improving but I think the next step you will have to reach when you translate is to re-think your sentence in french instead of using your english sentence and trying to stick close to it. "On Saturday" is a formula that has no real equivalence in french so french people would write/say something like "Samedi, je suis allé au marché". In the same vein but reversed, french people would be more likely to say "j'ai entendu dire" instead of "j'ai entendu". I'm not sure if "j'ai entendu" is wrong per say but it doesn't sound like "conversational" french I'm used to hear in Montreal. Do french people from other countries use that formula?