What shall I do to create a forum in my main website?

[nick_westlife]

I think you need to buy a domain and host it with a paid host as no one will buy products selled by using geocities...

geocities also offers paid webhosting. Actually I was talking about paid web hosting only.
Actually my question is, I have a website called "mysitename.com", and I want to attach a forum to my home page. To host forum, where shall I go? Can I simply upload forum software to geocities file manager(in my existing plan) to create forum page? or Shall I need to host it again with a new plan, with a new domain?

well I don't know much of geocities. But one is for sure. You needn't have to buys a new domain. Example: your domain is www.myname.com then surely your domain/hosting provider will provide you free subdomain and so you can keep www.forum.myname.com or else www.myname.com/forum (Like one which webmaster Money forum has) :wink:

Coming to the hosting no need to going to separate hosting plan.