what do i need to do because my iphone updated but turned off and want come back on

Try a reset. Hold the sleep/wake and home buttons together until you see the Apple logo and then release. The phone should reboot. This could take up to 30 seconds of holding the buttons together. If you are not sure how well the device is charged, before you attempt the reset, plug the device in for about 20 minutes and keep it connected to the charger when you attempt the reset.