e-mail problom with i phone

Hi i am Justin,

I have an i phone 4 s and i have a problom. It is my e-mail account G mail see over the weekend i looged in from you tube and it said that some one may have got in so i was re doing the passwrd and making it more safer like you chage your stuff on face book.. Now i been doing new passwords to vetery with the phone and keeps telling me user name or password is incorrect in the settings were do i go? becasue one part on the server in Gmail is gray out.

Justin