How much you’re willing to spend for someone to click your ad. This is set by you and plays a role in where your ad shows up.
Image ads, which show up on non-search engine sites. Anything from a small blog to the New York Times can show your ads (for a cost)
Non-image, text-only ads which can show up on search engines and non-search engine pages.
Cost Per Click, determined by your max bid and how well your page matches a user’s query.
CPM is an alternative to CPC, for CPM you bid for your ad to be shown to people and are charged regardless of # of clicks.
Defined by you, this is the goal of your site. It is most commonly a purchase, account creation, or email signup, but can anything else which you want to track.
Words and phrases which trigger your ads to be shown. These can be in the user's query or on the page where your ad displays, depending on the method of advertising you choose. You can bid different amounts for different keywords, and more popular keywords are more expensive, generally.
Specific sites or general types of sites which you want your ads to show up on. You can include or exclude by site name, subject matter, etc.