Do i have to pay to be in the first page of Google search or it will be itself there by the time
It depends on keywords you're looking for, content of your forum, the post rate (more the content will change more googlebot will come).
And it takes time, a lot of time.
Thank you for telling me that..if you have seen my forum there are no active members, thats why i am looking for advertising forums to advertise my forum so i can find some people who are interested to help mewith rhatlike moderators, administrators or just members