what does the number beside my nickname means??

It's called your User Rating and it is related to your participation. You will find that it increases: 1) When you post a discussion AND you have got at least one response 2) When you post a response or a comment to a discussion (but only for the first response and first comment that you make to that discussion; if you make a second response or comment, your user rating does not increase (but you will still earn for them, depending on the quality). See the FAQs on User Ratings for more information.

Yes It's the number of discussion you post & participate or comments. Soon they will rate you on the top of your name with a star.It's one to ten scale.