Let's take the example of chlorine. Chlorine has an electron configuration of
The noble gas one energy level (row) above chlorine is neon with an electron configuration of
To write the noble gas configuration for chlorine we replace the electron configuration of neon
giving us an a noble gas (core) notation for chlorine of
Typically, chemists do not use noble gas notation for the first 18 elements.
To illustrate a more complex configuration let's take a look at element #51 antimony (Sb).
The electron configuration is
I hope this was helpful.