How to make Enemy AI and Health

Hey, I have a school project that I have nearly finished, I've completed the world and just need my enemy. My overall goal for now is to complete my enemy and give my player health so that I can be attacked (touched) by my enemy which decreases my health in turn resulting in me dying and restarting the level. I was wondering, cause I basically no next to nothing about Javascript or C#, would anybody be able to help me with these two things?

In terms of the enemy, I basically want him to walk around on his own but when I enter a certain radius of him, he starts chasing me (which would then turn him form his idle animation to his running animation) then if he touches me, my health would start to decrease.

Thanks so much to whoever can help with this and I'll add you to the finishing credits or something to thank you cause I imagine this is a complex thing to do.

-Brandon