explainer
noun /ɪkˈspleɪnə(r)/
  /ɪkˈspleɪnər/
- a person who explains a concept, topic, situation, etc. 
- He's a good explainer and always gives lots of examples to illustrate what he's talking about.
 
 - a video or a piece of text that explains a concept, topic, situation, etc.
- Here's a video explainer on how the nervous system works.
 - This helpful explainer sets out the key issues surrounding the elections.