Hi Vishnu,
Some information about the this is as follows
Bidders are those who submit responses for RFX and bid for reverse auctions. If the bidder's RFX response or bid is considered to be the best and accepted then a supplier relationship is established with the bidder. The person who would be placing bids on behalf of the organization is known as the contact person.So contact person is the person who is associated with the bidder and who can actually login to the portal search for the RFX and submit the bid.
Portal Provider is a company which hosts the portal for the company. If the company is hosting their own portal site then there is no need to create this type of business partner. Instead during the RFX creation process add a normal bidder who is there in the system.
Regards
Pramod