How do I have a password field say "Password", which changes to password characters as you type?

How do I have a password field say "Password", which changes to password
characters as you type?

It's a flat design, and I've kept the words "Username" and "Password" in
the form items themselves. The dilemma is how do I get it to show
"Password" but then as you type show the password characters?
Thanks in advance :-)