Types of sources:
Primary VS secondary source - A primary source belongs to the person who created it. So think of the texts you send. Your texts are primary sources because you created them during your lifetime. They are documents of a specific time. (Diaries or documents or reports created by historical folks are also common forms of primary sources.) Check this out.
Secondary sources involve taking primary sources and making meaning out of them. If your friends decide to take your texts, write out all the stories around those texts, and publish a book about your life with them, they've created a secondary source. Here's some more help with these concepts.
Popular source VS scholarly source - A popular source is designed for a general audience who does not have advanced knowledge of a particular subject. They are used to entertain, inform, and sometimes, to heavily persuade the reader in a biased manner.
A scholarly source is designed for a specific audience who has advanced knowledge of a particular subject, or for those studying that subject. They are used to share findings or developing research in specific areas of study. An excellent chart demonstrating how these differ is located here.
Especially important with scholarly sources is the process of peer review. If you have traded work with a classmate to check for errors, you are already familiar with the concept. Peer review keeps academic publishing accountable. A researcher shares their work with others who are also experts in their field. The reviewers check for errors, unanswered questions, etc., and the process is repeated.