The edition (e.g., Enterprise Edition, Developer Edition) is readily identified by examining your browser's title bar or running a query: SELECT Id, Name, OrganizationType FROM Organization
But finding the version is a bit trickier, with no "official" method to reference. You can try one of the three methods below:
- Switch to one of the standard, out-of-the-box apps (e.g., Sales), and look at the app logo
- Create or edit a formula field, and look for the largest API version in the $Api object
- Generate an Enterprise WSDL (Setup > Build > Develop > API) and look for the SOAP service endpoint location
You can convert the API version number into a release using the assumptions that Salesforce pushes three releases a year (Winter, Spring, Summer) and that each release corresponds to a new major version number. For example, we know that Winter '14 is API version 29.0. This means that 28.0 is Summer '13, and 30.0 will be Spring '14.