Copyright

Copyright is the legal right that protects original creative work, including software and its source code. The creator can decide how the work is used.

There is no registration process and no form to fill in. Copyright exists from the moment a piece of work is fixed in a form that can be copied, such as a file stored on a computer or a paragraph written in a document. Adding a copyright notice is optional; the right exists whether or not the notice is there.

Work, not ideas

Copyright protects the actual work you produced, not the idea behind it. Another person can make an independent piece with a similar purpose as long as they do not copy yours.

For example, imagine you build a small app that reminds you to water your houseplants. Your code, and the way you have written it, is protected. A developer who sees your app and then builds their own version from scratch, with different code, has not broken your copyright, even though both apps do a similar job.

Software

Patents are not the main protection for software; copyright is. This covers the program's source code, so nobody else is allowed to reuse your code without your permission.