what happens when we reset our device? what may occur? memory loss or something?

When you reset through settings it just restores your iPhone's settings to manufacture settings. If you are talking about reseting in iTunes you are deleting everything off of your phone, and then reinstalling a fresh firmware and your old backup. If you are referring to holding home and lock until your iPhone turns off and then turns back on it reflashes your phone and does a total reboot.

Hi.. i want to ask, why i cannot turn off my phone? and it keep searching for signal.. i dont know why. please help