Hi. I am trying out for a talent show and I really wanted to sing an origanal song but I have no idea how to write a song. Can someone help me write it?

Part of talent is that YOU write the original song. Songwriters ask for thousands of dollars for their work, so no one will write a song for you for free.

Why not sing an old song that no one has heard for years and years? How about "Sh-boom"? That's a crowd pleaser. Here's a site with more:

100 Greatest Uptempo Doo-Wop Songs

Good luck at the talent show!