What does a supporting text mean? provides two valid reasons with explanations and supporting text with accurate details corresponding to supporting text. paragraph(s) show evidence of planning. what does this mean? like what i have to

I'm assuming supporting text is referring to supporting text evidence. Basically meaning taking excerpts from the provided text to prove whatever you are claiming in your answer. 
What you have to do is write a paragraph (or longer) that provides two reasons of whatever the topic is.You must include with these two reasons evidence or quotes from the text and plenty of details about your answer. You must also show evidence of planning, or show that you structured or brainstormed before beginning. For this you can either make some sort of chart or graph, or just make bullet points of main ideas and details.

I hope this helps! Let me know if you have any more questions :)