An assertion is more or less a statement of opinion/belief. So, you will be stating your views or ideas on foreshadowing, symbolism, and imagery in "The Scarlet Ibis".
If you have discussed the story, you know that Doodle's death is foreshadowed at several points. So, your assertion about symbolism would be, "Doodle's death is foreshadowed by...."
There are lots of assertions you could make about imagery in the story. Find places where imagery is used in the text (hint: there's a lot of imagery connected to Doodle,s appearance/movement and a lot of imagery connected to nature). Then decide why the author chooses to use it. Your assertion for imagery could be something like, "The purpose of imagery in 'The Scarlet Ibis' is..."
Your symbolism assertion will revolve around the Ibis itself. A symbol is something that represents something other than itself. What does the ibis seem to represent to the reader based on its physical appearance, its unusual location, and its death? Your assertion could be as simple as, "The ibis symbolizes..."
this is super hard and don't sweat if u suck at it cause i do too