The primary market refers to the first time artwork is introduced to the market, usually by an artist selling work to a collector through their gallery.
Galleries are the lifeblood of artists, helping them shape their voice, offering feedback, and managing all their transactions, marketing, exhibitions, and pricing.
The secondary art market refers to the resale of artwork from one owner to another. This usually is from a seller to a buyer through an auction house, but can also be collect to collector, or facilitated through the original gallery or an independent dealer.
Christie's and Sotheby's are the two largest players. Others include Phillips and Bonhams. Visit their websites for a calendar of sales which you can attend by RSVPing.
To follow investment grade works (works above in the hundred's of thousands of dollars), check out the TEFAF, Art Price, and Mei Moses Art Index annual reports