Disclaimer: IANAL. That said, here are some random thoughts on the topic:
The term "Intellectual Property" bundles together many kinds of law: patent, copyright, trademark, and trade secrets, among others. Applying a license to a work you create will affect how your work can be used. Because each license allows for different uses of your code, how you apply the license is usually specific to which license you choose. For example, information about how to license your code under the Apache 2.0 license can be found at http://www.apache.org/licenses/. Note that projects managed by the Apache Software Foundation also require each contributor to grant the ASF copyright for the work. Granting of copyright is separate from the license.
I'd recommend reading Van Lindberg's "Intellectual Property and Open Source" to learn some terminology, and if you have significant commercial interests related to the code, spend a few hours with a lawyer.
