I need help with the 6 types of chemical reactions
I can't ever decide which is which when I look at a problem. Also I don't get
Example: Mg+HCl--->MgCl2+ H2
Where did those numbers come from ?

It isn't Mg +HCl it's Mg+2HCl = MgCl2+H2 Magnesium reacts with Hydrogen Chloride to produce Magnesium Chloride = Hydrogen. It's all about moles.

That's balanced right?

Yes, balanced equation. Element count on each side must be the same-1 Mg, 2H and 2Cl = 1Mg, 2Cl and 2H