There are some rules for plural -- there are like 11 standard ways to make plurals -- though of course there are exceptions. But i think youll find that major exceptions in german will be a little less frequent than those in english. German grammar tends to be pretty strict.
It looks as if you have moved on to Esperanto, ThomasBook1, but to answer your question, I've pasted an excerpt from another thread:
... You're really just going to have to memorize the gender of the nouns, but, until that happens, you may benefit from reading through a couple of posts on this topic. You may find some overlap in these two posts, but I thought they were each deserving of a reference, so I've listed them both:
The page at the link below is also a good reference:
Hope that helps you or anyone else who asks this question.