Changed index.php and localhost:8888 is blank

I am using MAMP on Mac for WordPress. I successfully built and uploaded the website but it didn’t show on the server. So I changed the file index.php file, trying to solve the problem. It turns out the problem didn’t get fixed and my localhost:8888 is a blank page now. I changed the index.php file back but the page is still blank.

I can access to localhost:8888/wp-admin and edit everything there. And when I customize the website the site looks fine. However when I click Visit Site the home page is blank again.

How can I fix this problem? And how can I make the website show when it is uploaded to the server?

Thank you very much!