How to add to php get home url to make links to new pages?

I'm currently working on a website that's hosted on our development server, I want to make some links that won't break when I move the site onto the new domain, so I plan to use to first get the root url, but how can I use that to make a link to the page at www.domain.com/blog?

Thanks a lot, hope that makes sense, couldn't really find a better way to word it!

Thanks, Ethan