cant send e-mail says user name or password incorrect

That means exactly what it says. In your outgoing mail settings (SMTP settings) either you don’t have a user name and password, or one or the other is incorrect. Outgoing mail and incoming mail are separate operations, and each must be set up individually.

The easiest way to fix it if the account is an IMAP or Outlook account (go to Settings/Mail/Accounts and tap on the account to see), just delete the account, restart your phone and add the account back.

For a POP3 account you will have to go to the same place and edit the outgoing mail server settings.

Not quite sure what you're asking without more details, but if you need to sign in to your email go to Settings > Mail > Accounts > Add Account.