Mikey,
To use MAMP, you simply need to start MAMP and then set a few defaults - such as where localhost (your server root) will reside. You probably will want to map it to your "sites" folder. Then I would reset the Apache/MySQL ports to default so they become 80 and 3306 respectively. If you set your localhost to map to the site folder and pretend you have a site in a folder within called "mysite", the path in your browser becomes "http://localhost/mysite/"
Regards,
Brian