[SalesForce] Visualforce page: access from a guest

When you create a community inside Salesforce ,A salesforce site is automatically spun for you for accessing the community without login credentials as a guest user .

Lets take an example community set up to understand this

I have the communities as in screenshot

When i navigate to sites via set up menu,I see sites are already created by SFDC

The error is complaining your page is not accessible for your site .Below screen shot will help you on how you will add your VF to provide access to guest user

Do communities evaluate the Record requested when determining if a page should be accessible?

Yes they evaluate access based on the user/guest user. check documentation here on how they check page/record access.Below is how the hierarchy of access works.

We have decided to set the community global default to private, and then make the pages we want to display public in their page settings, but for the pages with master-detail relationships, we cannot set that setting. The message is Page Access: Your community-wide access level is set to Requires Login. However, access to this object page depends on your Salesforce security settings. Not sure who can see what? Ask your Salesforce admin.

For you to allow guess users to access object pages you need to enable this check box in community builder settings.Once you do this and if you have opened up guest user access to the record in question they will be able to see the information.

What you have done is the right way to do Make external sharing settings private and allow access to the specific records for the guest user.

Final Note: Do Publish the community before testing out these changes.