In my English learning book the exercise often reads:
Read the text opposite and answer the questions below.
What does the word 'opposite' mean in this sentence?
"Opposite" in this context means "across from this text you are reading right now". It may mean on the other open page of the book, in a sidebar column, or just to the right or left. The root of the usage is that the text you're being instructed to read is positioned "opposed", or counterposed, to the text doing the instructing.