Multiple seeds for random numbers (C#)

I am uncertain as to how to ask this question, but I shall do my best.

I am trying to design a set of subroutines which each have a set random seed. i.e. Set 1 will always use seed A, Set 2 will always use seed B, etc. (these seeds are established elsewhere by a core seed which is more randomized). This is being done so that it can produce reproduce-able results given the same core seed, while also giving the appearance of pseudo-random numbers.

See, my problem is I don't understand how RNG work. I have no educational background in programming, just a lot of hands-on so I never got the theory behind the application. Trying to read the wikis is like reading exceptionally dry textbooks: cannot swallow what they are saying.

There are going to be multiple sets of numbers floating around in this code, and what I want to prevent is one set of 'random' numbers messing up the others, without having to save everything in arrays from the beginning (which would be extremely RAM intensive).

I don't want to move forward without having a firm grasp on how RNG work so I can make sure if I pass seed 012045078096100 into the RNG, then have to run some other code for random numbers because of procedural events, then return to the RNG to finish the details that it won't produce the same results as if those procedural events never occurred; where the sequence of numbers will be the same regardless of outside calls to an RNG. Is there a way to isolate a given RNG for a specific purpose, essentially running multiple RNGs: some with seeds, some with timer-based random seeds?

So, my question is: Where do I begin to learn about this? Going back to school is not an option (time, money), so self-education is my only path. Any pointers would be appreciated.