Explain RSA in a math language that I can understand

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Having not a super high-level background in math, I can't understand several parts of RSA.

I know that you select a number n, and two numbers e and d.

Then you have ed= mod(φ(n)), which looking it up means that ed is equal to the number you get when you count in a "modular way" in a rotation of φ(n), like a clock, except instead of 12 hours, you have φ(n) hours.

Looking up φ(n), it seems to count the number of relatively prime numbers to n.

Then you tell everyone e and n.

Then to send a message, you make sure the message number and n are relatively prime to each other, and that it's smaller than n (also greater than 1).

Then you do R = M^e mod n, and I am not really sure what is going on at this point.

And then you decode the message with R^d mod n, which again I don't know what is going on.

And I am now lost.