Email Validation Strings

I've got a couple of strings I use to validate emails.

I have no idea what either of them do or what they mean! I found them, they work, so I use them!

Could somebody let me know what these mean? My guess is that the longer string is better, simply because it tests more thoroughly, but I could be mistaken.

String1 = ""^([a-zA-Z0-9_-.]+)@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.)|(([a-zA-Z0-9-]+.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(]?)$""

String2 = "^w+([-+.]w+)*@w+([-.]w+)*.w{2,}$"