Here is a proposal template ( without the explanations.
Out of the 15 possible sources you found for your proposal, you should end up with 7 to 10 VARIED (NOT all Internet sites, for example) sources - including professional journal articles and professional publications, Internet sources, and possibly (but not required) an interview.
It is a balancing act to find sources that you can understand - that relate to your level of study in your discipline, and, at the same time, challenge you intellectually.
This information should be on a separate page called References.
Abide by all of the APA format guidelines for the reference page.