"Please do not tell them."
Right, but I am confused when to use it. When I want to say, "I don't see" it is "我不看" or "I don't listen" is "我不听." But here 告诉 is "to tell" or "to inform," so I felt like to "not tell them" would be ”不告诉“ but I was wrong, it's "不要告诉” and I don't understand why the 要 is required.
I'm not a native speaker, but from what I understand is that the 不要 is more into a demand. You're right about the 不看 and 不听, both means "not seeing" and "not listening", and both are not a demand. No one is telling you must not see or listen. The 不要告诉 is a demand to another person not to tell the other. Again, I'm also still learning. Correct me if I'm wrong. Happy learning~