Getting started:

• Where do I get my php/html files?
• What type of files can I upload?
• What versions of php are supported?

About the site:

• How much does it cost?
• How secure are my files?
• Is it production safe?
• How does it work?
• Coming features

About the optimizations:

• Print statements into echo statements
• Double quotes into single quotes
• Period concatenation into comma concatenation
• Relative paths into direct paths
• Optimize tag attributes
• Remove unnecessary attributes

About the warnings:

• You may have javascript before style information
• Global variables copied to local variables
• MySQL queries inside loops
• MySQL queries that might be selecting more than necessary
• Image tags that are missing one or more dimensions
• Stylesheets possibly outside of the HEAD
• Javascript possibly in the HEAD
• Internal stylesheets
• Internal javascript
• Duplicate javascript files possibly
• Duplicate stylesheets possibly
• Duplicate javascripts possibly

It should be. However, it's strongly encouraged that you review and test your code before putting it into production. For many reasons, no part of your code is ever executed on our server.