An apostrophe looks a little bit like a comma but higher on the line, about as high as your tallest letter (ascender).
Apostrophes for contraction - This shows when we have missed out some letters and "squashed" 2 words together. For example, "don't or can't".
Apostrophes for possession - We can use an apostrophe to show when something belongs to someone or something. For example "Duncan's crayon" - the crayon belongs to Duncan.
Go through the book (you can use the Youtube version for this) and see if you can find any apostrophes.