what do we come to know about the three friends from their attempts to open the pineapple tin ??

This is very much a comedy of errors as it brings out how these men are not the most handy when it comes to practical concerns like opening a tin. Check this out:

http://www.gradesaver.com/three-men-in-a-boat/q-and-a/describe-the-episode-of-opening-of-pineapple-tin-230426