"Its" is a possessive pronoun of "It". Example: Its rear tire is out of balance. "It's" generally translates to "It Is" or "It has". Example: It's about time you got home.
"Explain" means to give additional information, such as details, rationales, or other clarification of an existing issue. It implies teaching, instruction, or the reiteration of knowledge.
"Discuss"...
While both DO and MD are physicians, DO is a doctor of osteopathy, meaning to treat the body as a whole, and MD is a medical doctor who treats the ailment/illness in a "targeted" manner.