H.I.D INSTALLATION PROBLEM

I have a hi/lo H.I.D and i need to install a relay,can someone tell me how to install that???

In my instruction they ask me to install relay AND diode,
diode? what kind of diode? and where can i bought that?
how to plug that? i'm lost

I can't take the + direct from the batt,i think i have to pass via the light switch...right?

Any help is appreciate.

I don't have any relay with the kit,you can see exactly what i mean if you go at
www.americanmuscle.com.They post the instruction on their site.