I don't have my reference manuals nearby, but dig up some good assembly programming basics guides they should help.
I'm probably wrong, considering my day, but:
We control EIP which is the next instruction pointer and tell it where to point. After it has pointed where we tell it to, the CPU resets EIP to the next instruction in the list (which is, in this case, jump to the location stored in ESP).
ESP is the stack pointer, and points to the highest (lowest?) point on the stack. That we are jumping to ESP is irrelevant (normally I work it so I can jmp eax, and it interacts the same way). As far as EIP is concerned, it's just one more instruction to execute and it just happens to be stored in the ESP.
Anyway, that might be absolute garbage, but it's a start. Read an assembly book, or wait for someone with a guide handy to refer to.