i need to build a forum website....can anyone help.

From scratch? I think they have tutorial about it on tutsplus.

Otherwise, you can use bbPress, vBulletin or phpBB.

If it’s from scratch welcome to permission hell, otherwise it’s just another dynamic site with database of users, permissions , threads, comments and anything else you may need.

Otherwise, don’t reinvent this wheel it’s been around for too long to bother.

There's a myBB also which is open source and nice.
Though if you need it to be a professionally developed and licensed one, go for vBulletin

if you're a fan of php, and like Laravel i would recommend october cms it has all the user oriented stuff and also a forum module that will get you in business quite fast https://octobercms.com/

Also i could help along with building it thanks to working a lot with laravel.