I've heard is extremely messy. Do men release a mive amount of semen or something?

I'm not experience in the dept. (ahem...virgin). I'm getting married very soon & I've been hearing that is messy & you have to immediately clean up afterwards. One friend even told me that after one morning she went to work & leaked so much fluid that she had to change her pants!!! How is this possible, I thought men only released about a tbsp of sperm..I've just been thinking about how much of a mood killer "messiness" must be. I've always imagined me & my honey just laying there afterwards & falling asleep in each others arms...someone please clarify this "mess".