I chose the perk Blood Healing. So how do I kill someone with a "Power attack bite"? I don't see no option for it in my D-pad. I don't even know how to bite anyone.

I saw the vidoes of the VL biting the neck of some people. Is this it?

Also, how do, or what am I suppose to do, to decrease the stages of being a vampire?

When you're fighting in the melee mode, melee power attacks that kill people will sometimes do a bite finishing move. That is the power attack bite.
So effectively, when in melee mode use power attacks to finish people off, & you'll heal sometimes.

Thank you Jefferson. I will try that. Another quesiton then, is do you level up or get xp points in melee mode as a VL? I read somewhere you don't, so I don't use melee mode offten, and I find it really weak. How do I become stronger in melee?

No problem, & you do gain perks in melee mode. Just slower. Since you gain perks through power attack bite kills, & drain kills.
Since you can always choose to kill someone with the drain attack, but there's only a chance that the bite kill will activate, you generally gain perks much quicker in the magic mode.

As for melee being weak, I honestly don't think so. I had more luck with it, than with the spells.
But the poison talons, & the bat cloak make it a lot deadlier. Having a sustained damage AoE, & a DOT effect that you can apply with each melee attack is pretty handy.
Basically, to power up the vampire lord's melee abilities, stick to the middle of the perk tree.

Thanks again for the quick responses. I will try and do as you say.

Thanks again. Off back to playing some Skyrim.