To find friends to invite, go to your Club or Group page, and click Group Members, to see a list of other members at your club.  Then click on View Profile, to open the Profile of the selected Member, then click Send Friendship Request.  This will send a Friend Request to the selected member.  That pending Friend Request will then appear on your My Friends page, as a Pending Friend Request, until that member Accepts or Declines the Friend Request.