What is Number Distributions, Entropy, and Repeatable Simulators?

I have been studying PRNG algorithms and how are they work (I am interested in to understand the internal working of them). I have studied https://en.cppreference.com/w/cpp/numeric/random and a bunch of questions raised in my head.

1. What is the difference between Random Number Generator, UniformRNG, and PseudoRNG?
2. What is the number of distributions?
3. What are the repeatable simulators?
4. What is Entropy?
5. What is the difference between std::mt19937_64 and std::random_device?
6. Why we should use uniform_int_distribution and this kind of class and where we should use it?

I am new to Stackoverflow. Sorry if you find out this question too basic.