Different people involved in affiliate marketing :

How Does Affiliate Marketing Work?

Here is my simple explanation :Website owner of affiliate marketing agrees to promote the product from a merchant with commission from every sale. There are two kind of product to promote, one the physical goods meaning goods that are delivered via a shipping company or postal mail. Another kind is downloadable products in digital format such a eBooks and software. 

Different people involved in affiliate marketing :Person owning the website to promote the product is called affiliate marketer. Person owning the product is merchant. Person who has the list of merchant willing to sell their product online is affiliate network (CPA Networks).List of CPA Networks
Ad Drive, Ad marketers, Ad Paid, Ad reporting, Ads4Dough, Adteractive, Affiliate.com, Affiliopolis, Affiliate Fuel, Affiliate Window UK, Affiliatebot, AffiliateClick, AffiliateFuture UK, AffNet, AmpedMedia, AKMG, AsSeenOnTV, Avant Link, AzoogleAds, Aquasis Media, Axill, Blue Phoenix, Bridaluxe, BulletAds, Cash for Clicks, CashRing, Casino Coins, Casino Paycheck, Casino Rewards, CheckMyStats, Cibleclick International, Commission Junction, Commission Junction UK, Clickagents, ClickBooth, ClickBank, CXDigital, ClickXchange, clixGalore, Commission Shore, CommissionSoup, Copeac, CPA Empire, CPX Interactive, CoregMonster, Cunna, CutsPM, Cyberbounty, CyberAffiliates, DarkBlue, DirectLeads, DirectResponse, DrumCash, Element5, eTology, Extremerevenue, FastClick, FineClicks, FloppyBank, FluxAds, Fosinaoffers, GlobalDirectMedia, Healthy Payout, Hexpress, Hydra Network, iCommissions, Income Access, IncentaClick, Intela, Iron Offers, Kolimbo, Lead Hound, Leader Markets, Lead Rewards, LeadsEffect, Leadsponsors, LinkConnector, LinkProfits, LinkShare, LinkSponsor, LynxTrack, Market Health, MaxBounty, Media Whiz, Media Trust, MetaReward, ModernConsumer, MPORT, Myresellers, NeverBlue, Offer Fusion, OffersQuest, OfferWeb, One Network Direct, Panthera Network, Partner Weekly, Partner2Profit, Performics, Pepperjam Network, PrimaryAds, Prospectiv, Quinstreet, ReferBack, RegNow, Revenuecpm, Revenue Gateway, Revenue Pilot, Revenue Wire, RevResponse, Rextopia, Rocket Profit, Roirocket, Rowise, Search4Clicks, SearchCactus, SellShareware, ShareaSale, ShareResults, ShareBucks, Sitelink, SpecialOfferm, Sfpnetwork, Stellarads, ThinkHost, Totalaccessonline, Trade Doubler, TriadMediaSolutions, Unique Leads, ValueClick, VeraCash, VHMnetwork, WebSponsors, WebToolbars, xy7, Zan

All these affiliate networks have different offers and different Commission type (CPL, CPA, CPS etc), Payment method (Check, PayPal etc) Payment threshold ($25, $50, $100) Payment frequency (Net 15, Net 30, Net 45). So selecting and signing up with particular affiliate network should be done as per the convenience among the varieties available.