If you own the copyright to your work, you can choose to apply a license to your work. Applying a license gives potential users permission in advance for how they can use your work, and removes fear, uncertainty, and doubt. For example:
Licenses can make your work more discoverable to unanticipated readers, and encourage innovative uses - such as teaching, text and data mining, and meta-analysis.
Here is some information about different types of licenses for different types of work.