With a Creative Commons (CC) licence you can specify how your publications (or other works) can be used by others with regard to copyright. You can, for example, allow your articles or illustrations to be shared, repurposed and remixed by anyone. If you do not use a CC licence common copyright rules will apply.
The licences consist of 4 types of rights which are combined into 6 different licences. You can see the exact descriptions at creativecommons.org.
Please note that CC licences in principle cannot be withdrawn. This may be particularly relevant in the case of joint authorship (everyone has to agree) or open access publishing, where you should be aware that foundations and publishers may require that you use specific CC licences.