Here is the Explosion Box Birthday Card I made my co-worker for her birthday.
To make it you need a 7 1/2 x 7 1/2 piece of paper scored at 2 1/2 and 5" on both the width and the length.
Then you cut out the corners and fold it up.
For the top you need a 5 1/4 x 5 1/4 piece of paper scored at 1 2/8 and 3 7/8 on both the width and length. Instead of cutting the corners you need to fold them in at a diagonal and glue them down. There are plenty of tutorials on the Internet on explosion boxes, so I only attempted to explain the sizes as they differ depending on what you are exploding!