This page runs the original browser version of Cookie Clicker that Orteil released in 2013, the build from September 2013: the game reports itself as v.0.1251 under the save menu, and the update log on the left ends at 0.126, dated 6 September 2013. It is the old game Orteil kept online after the "big update" of 24 August 2013 launched the Cookie Clicker most people know today, so it is a much smaller game: one cookie, one store and eight kinds of building.
Click the big cookie to bake. Spend cookies in the store on the right. The buildings, in the order they unlock, are the Cursor, Grandma, Factory, Mine, Shipment, Alchemy lab, Portal and Time machine. Each one bakes on its own and costs more every time you buy another, so the usual rhythm is to buy whatever gives the most cookies per second for its price, then save up for the next tier. Your cookies per second are shown under the counter at the top left.
The update log tells the story of this version's end game: version 0.122 added a secret end-game item to counter the grandmapocalypse, and 0.124 made that Elder Pledge cheaper and had it buff grandmas and clicking while it is active.
The game saves into a browser cookie on this site, so progress survives a reload in the same browser, but clearing cookies wipes it. Export save and Import save let you back it up and bring it back; Reset starts over. Numbers On/Off and Flashing On/Off switch the floating numbers and the screen flashes. This save is separate from the modern game on the home page and cannot be moved into it.