No formalities are required. You do not need to register the software with an organisation and no indication needs to appear on the software - for example, a mention of copyright or the name of the author. However, for questions of evidence, it is very useful to mention the names of the authors in the software code, together with the date on which the software was created.
The software and its elements will be protected as soon as they have taken shape. Therefore, software that is not licensed may not be used (after all, the licenses serve to grant rights to a computer program).