Need Help Designing new Business Website

Hi Guys

Thanks for looking at my post, Im looking for some help to put my ideas and latest business venture onto a website.

I want a website that allows users to post assignments and other users to say they accept the assignment. In order to accept though you must be a registered member. The users must also be able to view the current assignments, categorys ect..

Do you know if there is any ready made add ons or software that would allow me to do this?

I know ive not explained this in great detail but if you need to know more let me know

Cheers