How does the timeskip get introduced

Work with me here, I wasn't around when Naruto went from P1 to P2 in the manga. So I'm just wondering how it works, will it just say "3 years later", or have another name. Like I fr dont know how it works or how they just introduce a timeskip. Im talking in writing any manga, not the plot or theories for before the time skip. Just how the timeskip will be introduced