How do I clearly write what is my idea verses what my sources’ idea? In other words, how do I keep my voice?

This may take some practice. If you have a source that is just spot on and there is no way you could re-explain it or integrate it with another idea, then quote the reference directly. You can also paraphrase the quote to keep the original sources ideas true, but this utilizes your own words as well; double bonus. To make sure you are properly paraphrasing, you can practice this by explaining, out loud, the concept without looking at the source. Whatever you say out loud to describe the original concept is what you should include in your paper; no synonyms here, just your own words.