How are values passed onto new variables from a main function to another function without using the same variable names?

I'm new to coding so please bear with me.

I'm currently trying to understand the flow and interplay between functions. I understand the basics of how we can call functions, pass arguments between and get return values etc.

However in deconstructing a solution to a practice problem to calculate splitting a bill, asking for user input in form of floats in the main function, these float variables are named

bill_amount
tax_percent
tip_percent

Inside the function to calculate the bill and split it we are using other float variables named

bill
tax
tip

While running the debugger to understand what's going on I can see how these variabels used in the "calculate" function are assigned the values of the variables bill_amount, tax_amount and tip_percent which we get via user input in the main function.

So my question is:

How does C know to pass the values from the variables in our main function to the calculate function? For example the value in tax_percent getting passed to variable tax, without specifically instructing the program to do so?

The program works just fine, I've tried googling to understand how this works and have been unsuccessful.

Solution

An assignment like x = a; is an instruction to set x to the value of a.

Given a function defined as void foo(int x, int y);, a function call like foo(a, b); is an instruction to:

Start executing foo.
Set the x of foo to the value of a.
Set the y of foo to the value of b.
Continue executing foo.

In a typical C implementation, the way this is done is:

When foo(a, b) is evaluated, the values of a and b are stored in places designated for passing arguments to functions, typically certain CPU registers or certain places on the hardware stack.
Where the machine instructions the compiler generates for the foo function need the values of x and y, they get them from the places the values of the arguments were put.