I know that if you add particles to the end of it, it can end meaning 20 different things. Mainly I’m not sure when to use it, or what feeling each particle will convey. (Explanations a caveman could understand, are appreciated).
It can have very different usages depending on when and where it's used. To keep things simple I'll just use a few examples.
By itself, そう basically can mean something like "That's right." So if someone says something to you and you want to say "that's right", or "yes", or anything like that, you can say そう, or pair it with だ or です like そうだ or そうです.
Now, when paired with a verb, it can become something basically meaning "that." So if you say "そうする", it's like "I'll do that." Or with "そう考えると…" it's like "If you think like that..."
As the last use I'll go over, it can also be used to refer to information you've heard about, or something that seems it will happen. For example "雨が降りそうだ", meaning "it seems it will rain."
I always think about it like "ach so" in German. The "so" in English can have a similar meaning too, I think. It takes creating some unconventional semantic connections, but I believe the intuition for そう can be built this way
To take ハデクヨン-san's example, 雨が降りそうだ would mean for me something like "So, it'll rain huh".
I know that u would already know what this means now, but just to help u if u come across any other sort of definition, u could use the dictionary, which is the green book in the right corner. Hope this helps!
