I have read that I cannot have a space when naming a php variable. Here is my issue. I have a form im working with that someone enters there first name, last name etc..

When im writing the php script can i use the underscore for the naming process.. In other words I know I cannot use $First Name as a valid variable. But can I instead use
$First_Name ? Or am I completely way off base here? Any help is appreciated.
Your mind is fine. Reality is what needs adjusting.