Migration from Webhost to Localhost?

Can anyone point me to instructions on how to migrate a copy of WordPress site from a web hosting site and load it onto my localhost? I am using MAMP and have wordpress up and running. I backed up the host site and downloaded, but not sure where to go from here? I want to work on changes in a test localhost environment, then upload to go live. I using Mac OS X 10.6.

Thanks.