It has been just over 30 years since the first "Magic Eye" book was released and I still can't figure out how these things work. I remember a time in the early 90s where the world was divided into two distinct groups - Those that are able to find the hidden 3d image and those who don't. We all had our unique method of seeing it - some would place the image close to their eyes and then slowly move it away, some would put their finger between them and the picture and then take it away and some could just do it on command.
If you have never tried it yourself, Here is what The internet says you're supposed to do. Good luck! it's worth it!