How do I make a conditional, to have different header info?

Hi,

I’d like to put a conditional or something like that in my header info, so that if it’s the main page being displayed, the robots meta would be this:
<meta name=”robots” content=”noindex,follow” />

but for all other pages, it’s this:
<meta name=”robots” content=”index,follow” />

What do I wrap it with? I read that conditional_tags page, but I think that’s about something else.

Thanks