Hi there are many register in x86 (i’m not sure other architecture use same convention) CPU, however there are 3 registers C programmer must know :
ESP or stack pointer used by several instruction to operate like pop and push, many assembly programmer love to use stack pointer for operating some value. ESP always point to used address.
Every function create new stack frame – also called EBS – , EBS contain function parameter or local variable.
EIP is instruction Pointer, address pointed by EIP containt next instruction executed by CPU.
Actually my description is far from complete, but it will enough for starting point to learn function call convention.