If you want to allow only Salesforce Community users to log in to your site, then you can setup Salesforce Community as your Identity Provider.
However, if you want both the standard users and community users in Salesforce to be able to SSO into your site, our Salesforce Community SSO add-on included in our WordPress SAML All-Inclusive Plan will help you achieve that.
In this solution, you will need to enter the standard Salesforce metadata and then add the community-specific SSO links to the Salesforce community SSO plugin.
Once this is configured, you can add separate links/buttons on your site using which the users can select if they want to log in via Community SSO or via the standard Salesforce SSO.
Please reach out to us at email@example.com for getting the Salesforce Community addon or if you have any questions.