System call is programming interface to the services provided by the OS. It is typically written in a high-level language such as C or C++.
The steps for making a system call:
1) push parameters on stack
2) invoke the system call
3) put code for system call on register
4) trap to the kernel
5) since a number is associated with each system call, system call interface invokes/dispatch intended system call in OS kernel and return status of the system call and any return value
6) increment stack pointer