I would like to create a website in which people of my town can get in contact to each other to find help, with a feedback system so that each user can gain or lose his good reputation depending on his activity and the feedback left from the other users.
So, resuming:
1)a user login/signup
2)the user1 can leave a post in kind of common board, asking for help; other users can reply to the post
3)then the user1 can leave a positive feedback to the user2 who helped him or a negative feedback if his experience was negative.
Do you know a script from which I may start to work?
Joomla + some of these extensions will be my first choice:
http://extensions.joomla.org/extensions/communication/question-a-answers
Some of the extensions are free, others are paid, its up to you which one fits your needs.
Joomla itself is user friendly enough to be handled without much coding experience. It have fair resource requirements so you may run it on a shared hosting till your community is growing.