It is a small pill "white" long and has (5421)on one side and (amb10) on the other

One question is, if you do not know what it is, why are you in possession of that pill?

A good resource is the PDR - Physician's Desk Reference - you can buy the paperback at Wal-Mart or one of the bookstores like Barnes and Noble. Or you can go to their website and research this:

Welcome to PDR.NET - The Physicians' Desk Reference web site providing prescription drug information and more (http://www.pdr.net/login/Login.aspx)

it is a small pill "white" long and has (5421)on one side and (amb10) on the other
It's Zolpidem Tartrate, 10mg - (commonly sold under brand name Ambien), a sedative-hypnotic used for the short-term treatment of insomnia (difficulty falling or staying asleep).

In simpler terms, it's a sleeping pill