"Service Unavailable" Error
It sounds like you're missing permission on a folder in the /craft directory. Best thing to do, is just retrace your steps by following the official install guide. 

I don't use MAMP though, so there might be extra stuff you need to do, but if you scroll down to the bottom of that page to the Additional Resources section. There are some other links to articles which might help, in particular this one:

Installing Craft CMS on Mac OS X Using MAMP &amp; Sequel Pro

If you do want to start again then you should be safe to delete the /craft folder and try again. Although unless you're missing files, you shouldn't really need to start again.