What you need to do is take one of the 3 Investigation samples and list it next to "My topic."
Then you need to find a source for your selected topic and follow the list in the first note card.
Usually the more information a source has about the author, and the publication, makes it more reliable.
Once you have that down, you need to provide the 2-3 sentences explaining why you think your selected source is valid and reliable enough to be used in a scientific research paper. You might google sources used in scientific research papers to get an idea.
If you can find sources with authors that have well known names or people who know a lot over your specific topic, then its more trustworthy.
For the next note card, do the same thing, but find another source. All your note cards will be over your one selected investigation sample.
So for instance, if you selected Electromagnet, then each note card will have different sources that mention anything having to do with your topic Electromagnet.
Hope this helps :)