find a particular song to purchase

JMTDRAGON wrote:

in I tunes store want to find a purchase an older song

JMT, I assume you are looking to purchase a song? Please follow whichever of the these 3 guides pertains to your situation:

Buy music from the iTunes Store on your Mac - Apple Support

Buy music from the iTunes Store on your PC - Apple Support

Buy music from the iTunes Store on your iPhone or iPad - Apple Support

Since you mention that it is an "older song," be aware that although the iTunes Store has a huge catalog, it does not have everything.

Try this -> start Music -> tap iTunes Store (side bar) -> tap Account -> show my account -> sign in.

(In the right pane)  -> scroll to Purchase history -> tap See All -> tap Last 90 Days, then select a different date range.

For example: 

You should know approximately what year you purchased.