views Relationships and argument?
Relationships are the way Views expresses SQL joins. For example, when viewing a node, you can add a relationship to it's author, pulling in even more data.

Arguments have been renamed "Contextual Filters" in Views 7.x-3.x, which is a better name. Basically, it's a filter that gets its input from the the page, either by the page's URL or the node or user being viewed, etc.