What do the different versions of Creative Commons licenses mean?

CC licenses are constantly undergoing revision processes. This results in new license versions (2.0, 3.0 and 4.0) over the course of time.

You can read about what has changed in the current version 4.0 compared to previous versions in this article by John Weitzmann on iRights.info: Creative Commons version 4.0 available: What's changing and what's not.

Older license versions:

sometimes contain different terms of use. It is therefore important to specify the respective license version. The version specified in the license note is always decisive. If this information is missing, the more recent version does not automatically apply. Rather, you should ask the licensor which license is meant.
have been adapted (ported) to German law. Versions 2.0 and 3.0 are therefore available both as an international version (e.g. CC BY 3.0 Int.) and as a German version (e.g. CC BY 3.0 DE).

users only have to comply with the terms of the last license/version granted, see section 3 lit.a. 4. CC 4.0. This rule facilitates the re-use of works that have been edited several times if the adaptations are licensed differently or have different license versions.
was not ported in order to avoid further fragmentation of the licensing landscape. There is therefore only a German translation of the current version, e.g. here for CC BY 4.0: Creative Commons - Attribution 4.0 International - CC BY 4.0.