"I believe superstitions" doesn't make sense, unless it was a person, it's basically like saying "I believe Jack".

Your understanding is correct. You can use "I believe" + clause OR "I believe IN" + noun. So you can say "I believe IN superstitions." You can't say "I believe superstitions." You can say "I believe superstitions really work" or something like that. "I believe" + clause has the same meaning as "I think" + clause. It goes before your opinion. "I believe in X" means you think X exists, or you think X is good or effective. Examples: I believe in God. I believe in Buddhism. I believe in unicorns. I believe in love at first sight. I believe in you. You can do it! I believe in eating a big breakfast. That way you won't feel hungry in the afternoon.

basically the meaning is the same,but the first ''I believe superstitions.''one is like she or he belive in any superstitions...the other one ''I believe in superstitions.''usually makes the person ask you what superstitions I think in your language In　is like で......I think in that part your dictionarie was exagerting the different