Heath Bar and Enemy

Im creating my first video game and i'm wondering how to create heath bar and some enemies that attack my main character. can you pleas help me with this.

Thank you :)

you may see this video: http://www.youtube.com/watch?v=MgRIwJrwwhE&feature=related and http://www.youtube.com/watch?v=kx31sZr_RJs hear you can fins the bar all about health